We conceived of this technical monograph on the July 16, 1990 Earthquake in a symbolic way as a medium by which we can remember those who have died, were seriously injured and have lost their loved ones. It is also a most fitting way to honor those who have helped us and who continue to help us through rehabilitation efforts or the studies that will tame earthquakes through preparedness and risk management.

Beyond this symbolic value, this monograph has utmost practical importance for the Philippines, a country which has now realized itself not only to be in the "developing" stage but also in the "disaster-prone" category. I am sure that the prospective readers of this Compendium share both our experience and concern, being members of the same "Ring of Fire" club or simply being concerned scientists and experts who believe that the search for knowledge is best served by sharing knowledge.

During the last two decades, the Philippines has suffered several devastating earthquakes. In 1968, 200 people died when the Ruby Tower collapsed in a 7.3 magnitude earthquake in Manila. More than 6,000 people died when a tsunami caused by a 7.9 magnitude earthquake in the Moro Gulf hit them in 1976. Then we had the July 16, 1990 earthquake whose devastation is so far unequaled in deaths, property damage and psychological shock.

The Department of Environment and Natural Resources (DENR) immediately initiated rehabilitation efforts after the July 16 earthquake. Livelihood programs for the victims and the rehabilitation of damaged watersheds were implemented. These, as well as the efforts of other government agencies and non- governmental organizations, however, are mostly of a curative nature and are not enough. There must be preventive approaches developed, if not against earthquakes (which we cannot prevent), at least in terms of early warning, land use planning, improved building codes, and the like. President Aquino thus signed on August 6, 1990 the Memorandum Order creating the "Inter-Agency Committee on Documenting and Establishing Database on the July 1990 Luzon Earthquake".

This Inter-Agency Committee chaired by DENR and the Department of Science and Technology (DOST) was tasked to undertake a unified, systematic and scientific documentation of information on earthquakes, particularly the July 16 killer quake for future planning and research. This is one product of the Inter Agency Committee.

The results of direct or related studies on the July 16 earthquake gain additional importance now that there is a need to again generate public interest and concern at the highest levels of government on how best to deal with earthquakes. Over the past months, the July 16 "Killer Earthquake" seemed to have taken the backseat in a series of prominent happenings including the eruption of Mt. Pinatubo and the national elections. For a short while, interest was revived by the release in the news media of the Marikina or "Punongbayan" Fault. But time has again eroded the attention focused accorded it. Those who have been to Baguio City, one of the most devastated areas during the July 16 earthquake, can hardly see any of the fear, sorrow, shock and ruins that characterized the city then. Almost everything has gone back to normal including the persistent and increasing applications for subdivision development in the steep slopes of the city.

We certainly do not want to generate intense interest and concern on earthquakes with another earthquake. The scientific information and the practical recommendations coming from the contributors to this monograph would surely be more than enough. In a sense, this is much better as we can look at what had happened and what we can do in a more objective, organized and even optimistic outlook.

To have learned nothing from the tragic events of July 16 would be callousness of the highest degree. To have done nothing to develop strategies to prevent injury and damage should another earthquake occur would be irresponsibility of the most serious proportions.

It may well be for us to remember how those trying to save schoolchildren pinned by concrete slabs, for lack of proper equipment, had to commandeer hydraulic jacks from passing vehicles. Those who have relatives in Baguio City can still recall the fear and the anxiety of not knowing what happened to their loved ones because of broken communication lines. In the mosaic of collapsed buildings we should again take note of questions related to siting considerations, risk assessment, structural foundations, architectural and civil engineering designs, buffer Ones and safety corridors.

Fulgencio S. Factoran, Jr.

Raymundo S. Punongbayan*, Rolly E. Rimando*, Jessie A. Daligdig*
Glenda M. Besana*, Arturo S. Daag*, Takashi Nakata**, and
Hiroyuki Tsutsumi**
*Philippine Institute of Volcanology and Seismology
** Hiroshima University, Japan

 

ABSTRACT

The 16 July 1990 earthquake (Ms = 7.8) produced a 125 km-long ground rupture that stretches from Dingalan, Aurora to Kayapa, Nueva Vlzcaya as a result of strike-slip movements along the NW segment of the Philippine Fault Zone and its splay, the Digdig Fault. The earthquake epicenter was placed at 15º 42' N and 121º 7' E near the town of Rizal, Nueva Ecija. The surface rupture essentially followed the pre-earthquake active fault trace along previously identified fault-related geologic and geomorphic features such as mole tracks, sag ponds, offset streams and fluvial terraces, shutter and pressure ridges, scarplets, and similar features, with only slight deviations in certain places. Secondary shears are present as localized features along portions of the main rupture trace. Ground rupture, which had a general trend of N 40-60º W, was predominantly left-lateral with measured vertical and horizontal displacements varying from 0.1-2.5 m and 0.2-6.2 m, respectively. Movement is concentrated along the main rupture although right-stepping en echelon faults and trace discontinuities interrupt the narrow fault trace. The spatial distribution of these en echelon faults suggests that these are surface expressions of fault bends and are more pronounced to the SE of the epicenter. Asymmetry of fault length with respect to the epicenter, rupture arrest and displacement distribution can be explained in terms of these rupture propagation barriers. Variation of horizontal and vertical displacement values with distance shows a wavy pattern with some observed scissor-like reversals in the vertical displacement along some segments of the fault. Rupture length and measured maximum horizontal (6.2 m) and vertical (2.5 m) displacements are within the range of values observed worldwide, for earthquakes of this magnitude.

Damage to buildings, infrastructures, and properties amounted to at least P 10B, a part of which was caused by ground rupturing. Structures directly straddling the ground rupture were totally damaged as a result of large lateral shifting and substantial vertical displacement. However, some houses within 1-2 m on either side of the ground rupture survived owing to their light-weight construction while those built of reinforced concrete within this zone suffered partial damage. Damages beyond 2m depended mainly on the structural integrity of the building and effects of local topography and ground conditions. These observations underscore the advantage of using lightweight materials for construction purposes as well as the need to observe sound construction and design of buildings particularly in areas close to the ground rupture and in places that may be affected by future movements along active faults.

  

INTRODUCTION

The 16 July 1990 earthquake (Ms=7.8) produced a 125 km-long ground rupture that stretches from Dingalan, Aurora to Kayapa, Nueva Vizcaya along a general N 40-60º W trend ( Figure 1 ). The earthquake epicenter was placed at 15º 42' N and 121º 7' E near the town of Rizal, Nueva Ecija and was caused by strike-slip movements along the NW segment of the Philippine Fault Zone and its splay, the Digdig Fault. Prior to the earthquake, portions of the Digdig Fault along which the ground rupture later formed, were mapped and documented by the authors and Takashi Nakata of Hiroshima University in connection with PHIVOLCS's active faults mapping project. The 16 July event thus provided the corroboration to the recency of the fault's activity. While no short-term prediction for the active fault was issued, its possible future reactivation was anticipated and presented as among the constrains in planning in a seminar conducted in Baguio City a month before the earthquake struck. The seminar was attended by planners and local officials from Region I and the Cordillera Administrative Region.

Mapping of the extent of the ground rupture and the documentation of fault-related features, aside from their value, will have significant implications for future land use and zonation planning, especially in areas close to or transected by active faults. Future movements of these faults are expected to follow pre-existing fault traces. Post-earthquake studies of the ground rupture may likewise provide additional insights into possible scenarios that might be expected when the Digdig Fault or other active faults in the Philippines next move. Furthermore, a study into the structural controls that affect rupture propagation arrest might provide us clues where strong ground motions that generally and enable us to identify sites along the fault trace where strong ground motions that generally account for a majority of earthquake-related damages might be expected

 

HISTORICAL SEISMICITY ALONG THE DIGDIG FAULT

Based on historical records, the 30 November 1645 earthquake may have originated from the same segment of the Philippine Fault which ruptured on 16 July 1990. This particular event is one of the most destructive earthquakes that affected Manila and large parts of Luzon, particularly in the uplands of Gapan, Nueva Ecija (SEASEE, 1985). The earthquake was so strong that at least 25 % of the houses in Manila along were totally damaged, leaving some 3,000 casualties. Earthquake-related effects ranged from fissuring of rice fields, landsliding that dammed rivers, and river-flooding of settlement areas. The earthquake was said to have been accompanied by a terrifying noise with felt aftershocks lasting until the following year. In 1892, a similarly strong earthquake caused extensive damage over a wide area in Luzon but accounts are unclear as to its possible epicenter. Some writers ascribe the earthquake to the Digdig Fault but the Puncan Church, an eighteenth-century church located just 200 m from the 16 July ground rupture, was not affected by the 1892 earthquake, yet collapsed during the 16 July 1990 event.

 

THE GROUND RUPTURE

Location, Style and Pattern of Surface Faulting

Documentation and field mapping of the active fault prior to and after its movement on 16 July 1990 showed ground rupture that the 1990 ground rupture closely followed the pre-existing active fault trace, with come minor deviations in places. Earlier movements of the active fault before the July 16 event left many geologic and geomorphic evidence, (such as mole tracks, sag ponds, offset streams and fluvial terraces, shutter and pressure ridges and scarplets) suggesting its recent activity. Because diaplacements along active faults essentially occur along or near the same fault plane and nearly always with the same sense of movement, the location and pattern of future strike slip faulting can thus be predicted within reasonably close limits by mapping such fault-related features.

A ground rupture is rarely confined to a simple narrow and distinct line. Instead, a complex fault pattern results where the main fault zone is complicated by branching and formation of secondary faults where lesser displacements occur. The main trace on the ground surface can be a single rupture or can consist of parallel, branching, or interlacing fractures, the width of which may vary from a few centimeters to hundreds of meters. In the case of the 16 July 1990 earthquake ground rupture, this zone is up to several meters wide depending on local ground conditions. The fault zone is generally narrower in areas underlying firm foundations (e.g., bedrock, adobe) than in places with soft substrate, such as sand and other fine sediments. Secondary faults in the form of synthetic, antithetic and subparallel fractures are as far as 300 meters from the main fault zone, as illustrated by the occurrence of secondary shears at Digdig, Carranglan, Nueva Ecija ( Figure 2 ) while branch faults may extend for a distance of 500 meters, as illustrated by the branch fault at Rizal, Nueva Ecija ( Figure 3 ). In places, the narrow distinct fault trace is often interrupted by en echelon traces and mole tracks ( Figure 4 ). In other locations, however, the compressional mounds between the ends of en echelon faults are not very prominent ( Figure 5 ).

Variations in Amount of Slip Along the Fault

In general, displacement is not symmetrical along fault traces but may reach a maximum or a minimum near one end of the fault and may show several high points of offset along the fault trace. For the 16 July ground rupture, movement was predominantly left-lateral with measured horizontal and vertical displacement values ranging from 0.1 - 6.2 m and 1.0 - 2.5 m respectively. The horizontal (H) and vertical (V) displacements when plotted against distance from the NW terminus of the ground rupture ( Figure 6 ) show a wavy pattern having points of sharp increase and decrease within relatively short distances. From NW to SE, a general decrease in horizontal displacement is observed except near the termini where both horizontal and vertical displacements approach zero values. Likewise, a plot of the net slip with distance from NW to SE ( Figure 7 ) shows a similar pattern owing to the predominantly strike-slip nature of movement along the ground rupture. Moreover, inherent difficulties in estimating full displacement in some cases and possible imprecisions in displacement measurements may also have contributed, albeit to a lesser degree, to the observed wary pattern of displacement values along the fault trace. Figure 8 shows the variation in the sense and amount of vertical displacement with distance along the ground rupture. From the figure, the amount of vertical displacement generally increases from NW to SE, accounting for decreasing H/V values ( Figure 9 ) along this direction. This is attributed to the tendency of the rupture for releasing stress by extension at the termination point rather than propagating further to the SE. The sense of vertical displacement is likewise not uniform (i.e., the upthrown block shifts from one side of the fault to the other) along the whole stretch of the fault owing to local ground conditions. Thus as a whole, measured displacement values and sense of vertical displacement along the ground rupture are characterised by unevenness and irregularities. Table 1 summarizes the displacement data along the ground rupture.

Length of Surface Rupture and Maximum Displacement Vs. Earthquake Magnitude

Empirical relations between dimensions of faulting and earthquake magnitude have been derived from studies of historical large earthquakes worldwide. Correlations have been made between magnitude and fault length and between magnitude and maximum displacement q (Bonilla). Figure 10 for example, shows one correlation between earthquake magnitude and length of surface rupture. Figure 11a illustrates the empirical relation between magnitude and maximum surface displacement while Figure 11b shows the empirical relation of length of surface rupture with maximum surface displacement. Plotting the pertinent data from the 16 July 1990 event into these figures indicates that the rupture length, magnitude and maximum surface displacement values for the 16 July ground rupture are within the range of expected values based on worldwide empirical data.

 

THEORY

Structural and Geometric Barriers

The presence of a barrier or a series of barriers along the fault rupture may constrain rupture propagation. Barriers could be in the form of irregularities along the fault plane as manifested by bends and jogs, a geometrical barrier near the rupture terminus, inhomogeneous barriers, or a combination of all of the above. Fault jogs and bends are usually classified as either dilational or antidilational. Dilational jogs are associated with small pull-apart basins while antidilational jogs are related to pop-up structures. Antidilational jogs clearly perturb ruptures and form obstacles to both short- and long-term slip transfer along a fault. However, dilational fault jogs seem to play an especially important role as preferred sites for rupture arrest (Sibson, 1987). Dilational fault jogs appear to behave as kinetic barriers which impede rapid slip transfer, but allow slip to occur slowly due to the difficulties of quickly opening a linking extensional fracture mesh in a fluid saturated crust (Sibson, 1987). Inhomogeneous barriers are those in which there are no obvious geometric obstacles and are related to differences in resistance to breaking along parts of a fault.

Rupture Propagation

Rupture propagation is a function of the magnitude of the applied stress, barrier strength and the areal extent of the barrier (Das and Aki, 1977). Crack tip propagation will be arrested if the areal extent of a barrier is large (Das and Aki, 1977). Hence, when the areal extent of the barrier is small, it is broken as the crack tip passes when the tectonic stress is relatively high or the crack tip proceeds beyond the barrier without breaking it when the tectonic stress is relatively low. However, when the tectonic stress is neither high nor low, then the barrier is initially unbroken as the crack tip passes but eventually breaks because of subsequent increase in dynamic stress (Das and Aki, 1977).

 

DISCUSSION
The southeast extension of the fault (with respect to the epicenter) is more restricted compared to the northern segment indicating that this part of the fault must have been more resistant to movement. Southeast propagation of the ground rupture could have been constrained by the presence of a barrier or a series of barriers.

Despite the considerable change in strike of as much as 30 degrees over a large area near Bato Ferry and Bateria and the presence of a series of more limited bends south east of the epicenter ( Figures 12 and 13 ), the rupture somehow still managed to propagate from the epicenter up to its south eastern terminus. The ability of the fault rupture to overcome such a bend can be attributed to the large stress applied during rupture propagation at this point on account of the proximity of the area to the epicenter. However, much of the available energy may have been conceivably spent to overcome this particular barrier thus slowing down rupture propagation in the process. In addition to this, irregularities along the fault plane might have contributed to the slowing down of the propagation causing it to proceed in a series of jerks. As a consequence of the rupture's uneven track, propagation was not smooth possibly resulting in the observed irregular values of slip along the whole stretch of the surface rupture. As the rupture encountered more barriers on its southeastward course, more energy was spent, until finally the remaining energy was no longer sufficient for the rupture process to progress beyond its termination point between Gabaldon and Dingalan. Furthermore, the presence of a formidable geometric barrier due to the abrupt bending of the Philippine Fault Zone from Dingalan to an almost southward direction ( Figure 14 ) may have greatly influenced the arrest and subsequent termination of the ground rupture.

In the vicinity of the epicenter near Rizal, the fault formed a branch with the main trace of the fault propagating farther northwestward while the splay did not go beyond Rizal town proper. The termination of the fault branch northwest of Rizal proper may likewise be attributed to the presence of a barrier. The nature of the barrier, however, is uncertain, there being no obvious change in rupture strike. However, intersecting and transverse faults along the trace of the rupture near the terraces at the branch terminus may have locally increased resistance of the fault to rupture propagation thus constituting an inhomogeneous barrier Additional evidence suggesting the presence of a barrier at the branch termination point is the high ground acceleration (g) value of at least 1 g in this area where many boulders where thrown-out as far as 20 cm from their former positions (Umeda et. al., 19?). Similarly thrown out boulders were also observed in Laur. Thus, high frequency waves induced by strong ground motion (Sibson, 1987) are enhanced by irregular rupture propagation with non-uniform slip due to the presence of a barrier (Aki, 1979).

From Rizal going northwestward, rupture propagation was relatively smooth. However, localized bends are occasionally encountered accounting for the non-uniform slip along the trace ( Figures 15 & 16 ). Near Cabalatan, Kayapa, the trace started to encounter significant bends until its terminus at Bisong, Kayapa ( Figure 17 ). The nature of the barrier at this particular point is quite unclear but it was apparently strong enough to resist extension owing to the already weakened applied stress.

Later, increased stress concentration at the northwestern terminus probably caused a sequence of aftershocks. In contrast, relatively few aftershocks occurred near the SE terminus of the rupture ( Figure 18 ). When a stress increase of great magnitude occurs, various things may happen (Aki, 1979). Stress could be concentrated near the stopping point and only partially released, thus accounting for the few aftershocks at the southeastern terminus. As the rupture could propagate no further, stress release in the form of greater vertical displacements thus occurred. In contrast, the spatial distribution of aftershocks at the northwestern terminus indicates a clustering near the end of the rupture zone and migration away from it, gradually extending the aftershock area. In this case, the stress concentration is relieved at least partially by brittle fracture. Alternatively the SE barrier may be ductile, relaxing stress by non elastic deformation, resulting in fewer aftershocks, while the NW barrier may be brittle and relieve stress by fracturing, producing numerous aftershocks in the process.

 

IMPACTS
The earthquake left in its wake about 1,200 casualties and at least P 10 B of damages to buildings, infrastructures, and properties. Part of this damage was due to ground rupturing, although no casualty was reported as a result of this particular hazard. Areas heavily-impacted by the effects of ground rupturing, were Rizal town proper and nearby towns of Laur, Bongabon, and Gabaldon to the southeast, and Digdig, Puncan (Carranglan), in Nueva Ecija, and Imugan (Sta. Fe) in Nueva Vizcaya to the northwest. Danger within the epicentral area were confined to a narrow zone 1-2 m on both sides of the rupture. Buildings and houses regardless of make and design directly straddling the ground rupture were totally damaged ( Figure 19 ), mainly due to large lateral shifting and vertical displacement. In many instances, however, a number of lightly-constructed buildings within this zone surprisingly survived ( Figure 20 ). In comparison, buildings made up of reinforced concrete within this 4-m zone suffered partial damage, underscoring the apparent flexibility of lightweight materials that tend to sway with and not resist, ground shaking. Beyond 2 m from the ground rupture but still within the epicentral area, damage to structures becomes minimal except for poorly- constructed buildings and on account of the local ground conditions. In places, substantial vertical movement along the ground rupture resulted to disruption of normal agricultural activities in the Rizal-Bongabon-Laur-Carranglan areas (Nueva Ecija) as formerly irrigated rice paddies can no longer be irrigated as these are on the upthrown side while those on the downthrown side cannot be planted to rice due to flooding ( Figure 21 ). Localised large-scale flooding occurred in areas where the streams and water systems were cut-off, dammed and at times, diverted by ground displacements ( Figure 22 ). Infrastructures such as roads ( Figures 23a and 23b ) and bridges ( Figures 24a and 24b ) along the ground rupture were also damaged as a result of both horizontal and vertical ground shifting.

Other earthquake-related damages can be attributed to strong ground vibration and related landslides and liquefaction. Vibration was widely felt in Luzon affecting areas more than a hundred kilometers away from the epicenter with the intensity varying with local ground conditions. Landslides affected Nueva Ecija, Nueva Vizcaya and Benguet. The effects of the landslides were more intense near the areas traversed by the ground rupture, areas undercut by streams, road cuts, and in highly-steepened slopes specially where the rocks are highly fractured and devoid of vegetation. Subsequent heavy rains carried down log-laden debris that sometimes resulted in the damming of river courses. Subsequent breaching of these natural dams resulted in widespread inundation of nearby settlements and agric ultural lands. Liquefaction and settling damaged mostly the swampy areas in and near Dagupan, Agoo and Aringay (La Union). In Gerona and Pura, Tarlac, liquefaction effects consist of subsidence, sand boiling and tilting of structures. Localised subsidence was also observed, in Metro Manila, particularly in the Cultural Center of the Philippines Complex along Manila Bay.

 

SUMMARY AND CONCLUSIONS
The ground rupture of 16 July 1990 Earthquake is not confined to a simple narrow and distinct line. Instead, a complex fault pattern resulted where the main fault zone is complicated by branching and secondary faults of lesser displacements. Secondary faults in the form of synthetic, antithetic and subparallel fractures are as far as 300 meters from the main fault zone and branch faults may extend for a distance of 500 meters from the bifurcation point. The narrow distinct fault trace is also often interrupted by en echelon traces and mole tracks reflecting the type of local material (e.g., firm vs. soft foundation) and the localised effects of rupture propagation. The ground rupture closely followed the pre-existing active fault trace, although minor deviations in places were observed.

The amount of surface displacement along the fault rupture varies greatly reaching a maximum or a minimum near one end of the fault and shows several high points of offset along the fault trace. Thus, displacement values and sense of vertical displacement along the fault is characterised by unevenness or irregularity, consistent with the location of barriers or asperities along the fault plane that prevent smooth rupture and displacement propagation.

Asymmetry of the NW and SE rupture lengths, irregular rupture propagation, termination, slowing down and jerky rupture propagation and high ground acceleration are controlled by rupture propagation barriers interrupting the trace and fault plane.

Damage to buildings, infrastructures, and properties amounted to at least P 10 B. a small part of which was caused directly by ground rupturing. Structures directly straddling the ground rupture were totally damaged as a result of large lateral shifting and substantial vertical displacement. However, some houses within 1-2 m on either side of the ground rupture survived owing to their light-weight construction while those built of reinforced concrete within this zone suffered partial damage. Damages beyond 2m but still within the epicentral zone was minimal depending on the structural integrity of the building and effects of local ground conditions. These observations underscore the advantage of using lightweight materials for construction purposes as well as the need to observe sound construction and design of buildings particularly in areas close to the ground rupture and in places that may be affected by future movements along active faults.

 

RECOMMENDATIONS
As shown by the results of this study, the 16 July earthquake essentially followed the previously-mapped active fault trace. The techniques and methodology used herein may thus be applied in the identification, delineation, and future studies of other active faults in the Philippines.

More detailed mapping of the location and areal extent of the 16 July ground rupture should be undertaken, especially where the latter transects or passes close to settlement areas. As far as practicable, it is likewise proposed that efforts be exerted to mark the location of t the ground rupture at strategic points for easy reference and shall serve as among the constraints in future land utilization planning and development in these areas.

Based on the observations of damages with respect to distance from the ground rupture, it is herein proposed that an easement of at least 5 m. on either side of the line of rupture be observed and strictly implemented for purposes of zoning and future land utilization and development scheme in areas transected by the ground rupture.

Existing codes and regulations governing the structural design and construction of buildings close to the ground rupture be reviewed, rectified, and most importantly, strictly implemented.

Specific sites along the ground rupture may be identified, developed, and preserved as national geologic monuments to instill awareness of earthquake-related hazards among the people and serve as concrete reminder of the 1990 earthquake and its damaging effects in view of the fact that disasters such as the 16 July 1990 earthquake are easily forgotten.

Multi-sectoral effort should be undertaken to embark on a nation-wide information campaign on the nature and hazards posed by earthquakes and their proper mitigation to educate the general public, policy planners, and decision-makers considering that the Philippines is an earthquake-prone country.

Existing contingency measures designed to cope up with disasters should be reviewed and modified to incorporate the various lessons learned from the effects of the 16 July earthquake.

  

ACKNOWLEDGMENT
The authors would like to acknowledge the partial funding extended to this project by the Department of Environment and Natural Resources through Secretary Fulgencio S. Factoran, Jr. without which this endeavor would not have been possible. The help extended by the following PHIVOLCS personnel in the preparation of some figures used in this paper are likewise acknowledged: Messrs. Eleuterio Diao and Reynaldo Macaspac, and Ms. Shirley Inmenzo.

 

REFERENCES
Aki, K. 1979. Characterization of barriers on an earthquake fault, Journal of Geophysical Research,84,6140-6148.

Beanland, S., Berryman Kelvin R., and G. H. Blick.1989. Geological investigations of the 1987 Edgecumbe earthquake, New Zealand. New Zealand Journal of Geology and Geophysics,32, 73-90.

Bonilla, M. G. and Buchanan, J. M.,1970. Interim report on worldwide historic surface faulting. U.S. Geol. Survey Open File Report.,32 p.

Besana, G. M., R. S. Punongbayan, J. A. Daligdig, J. V. Umbal, and B. C. Bautista. 1990. Preliminary analysis of the 16 July 1990 earthquake aftershock distribution in relation to ground rupture. 1990. Proceedings of the 3rd Annual Geological Convention, December 5-7.

Crone, A. J., M. N. Machete, M. G. Bonilla, J. J. Lienkaemper, K. L. Pierce, W. E. Scott, and Robert C. Bucknam. 1987. Surface Faulting Accompanying the Borah Peak Earthquake and Segmentation of the Lost River Fault, Central Idaho, Bulletin of the Seismological Society of America. 77: 739-770.

Das, S. and K. Aki .1977. Fault planes with barriers: A versatile model, Journal of Geophysical Research. 82: 5648-5670.

Nakata, T., H. Tsutsumi, R. S. Punongbayan, R. E. Rimando, J. A. Daligdig, G. M. Besana and A. S. Daag.1990. Surface faulting associated with the Philippine earthquake of 1990. J. & eogr., 99 (5): 95-112.

Punongbayan, R. S., and J. V. Umbal. 1990. Overview and impacts of the July 16, 1990 earthquake. Proceedings of the 3rd Annual Geological Convention, December 5-7, 1990.

Southeast Asia Association of Seismology and Earthquake Engineering, 1985. Edited by E.P. Arnold., Series on Seismology, Vol. IV: Philippines, Washington D.C.: Government Printing Office.

Sibson, Richard S. 1986. Rupture interaction with fault jogs. In Earthquake source mechanics, edited by Das, S., J. Boatwright, and C. H. Scholz. American Geophysical Union Monograph 37, p.157-167.

_________.1987. Effects of fault heterogeneity on rupture propagation. In The behaviour of seismogenic faults, Edited by A. J. Crone, and Omdahl, E. M. Directions in Paleoseismology Conference, XXXIXth Proceedings, p.362373.

Ziony, J. I. and R. F. Yerkes. 1985. Evaluating Earthquake and Surface Faulting Potential Evaluating Earthquake Hazards in the Los Angeles Region - An Earth Science Perspective (U.S. Geological Survey Professional Paper 1360). Washington United States Government Printing Office. pp. 43-89.

Ronaldo A. Arboleda and Ma. Theresa M. Regalado
Philippine Institute of Volcanology and Seismology

 

INTRODUCTION

The 16 July 1990 Luzon earthquake triggered and induced numerous landslides in northern and central Luzon, Philippines. Abundant landslides occurred northwest and west of the ground rupture along Digdig Fault and on a narrow zone closely following the rupture along the Philippine Fault Zone (Fig.1). Landslides were observed as far as Lagayan, Abra in the north; Agoo, La Union in the west and Dingalan, Aurora in the southeast. The landslide-affected region is part of the Luzon Central Cordillera Volcanic Belt and marks the junction of the southern end of the N-S trending Luzon Cordillera Mountain Range and the Caraballo Mountains. The uplifted mid tertiary volcano-tectonic complexes of the Luzon Cordillera Mountains join with the Pliocene-Pleistocene volcanic centers of the Caraballo Mountains to form a very rugged topography.

 

GENERAL CHARACTERISTICS

The total number of landslides that occurred was in the order of hundreds of thousands. These earthquake induced landslides occurred preferentially on moderate to steep slopes, drainage divides, valley heads and along road cuts with their crown coinciding with ridge crests. Most of the landslides were shallow, 0.5 to 1.0 m. deep, and composed in large part of surficial soils (Fig. 2). The relatively deeper landslides 2-3 m. deep, were composed of residual soils derived from the highly weathered and highly fractured rocks. In deeper landslides, a small volume of bedrock materials disaggregated and was incorporated into the failed mass Only a few block slides were observed, mostly along the roads leading to Baguio. A small percentage of the total number of landslides were remobilized old landslides. The majority of the landslides were translational.

 

EXTENT OF SLOPES AFFECTED

Initially, within 24 hours after the main shock, landslides occurred in discreet patches, affecting about 50% of the slope. The ensuing aftershocks and monsoon rains aggravated the situation by triggering more landslides.

Heavily affected by the subsequent landslides were slopes proximal to the ground rupture, and/ or slopes near or coinciding with dense concentration of aftershock epicenters and which experienced rainfall immediately before and days after the main shock. Denudation now ranges from 50 -90% of these slopes (Fig.3). Elsewhere denudation is lesser.

 

INVENTORIES OF LANDSLIDES

A. Maharlika Highway

A landslide inventory of a stretch of Maharlika Highway from Digdig junction up to Santa Fe was undertaken based on aerial photographs taken on the area 40 hours after the main shock and on field surveys (Fig.4). Considering only the landslides with a volume of at least 1000 cu. m., the volume of mobilized mass in this area covered by aerial photos was 5.52 million cubic meters. On a 40 km. road stretch, the highway was blocked by 13 major landslides and 8 minor slides with a total volume of 852,500 cubic meters. The densest parts, in terms of area affected per square kilometer, are found in Digdig and Anabat with a density of least 200,000 sq. m./sq. km (Fig.5). The major landslides north of Santa Fe and away from the rupture were mostly from slopes modified and destabilized by deep road cuts.

B. Baguio City

An inventory of landslides in Baguio City was likewise done based on aerial photographs taken on the area last January 1991 or roughly six months after the event, and on reconnaissance mapping (Fig.6). The earthquake-induced landslides in Baguio City and vicinity are shallow and translational. Some of the relatively deeper landslides were translational slides along pre-existing zones of weakness like fracture planes nearly parallel to the slope. The | sizes of the slides were relatively small - 20 to 250 m. wide, 50 to 700 m. long, with the S volume ranging from 500 to 170,00 cu. m. In contrast, the old landslides mapped are large, in terms of magnitude and area affected, and have rotational components. One of the old landslides affected an area of approximately 1.3 sq. km. None of the 16 July 19901andslides approximated the old landslides. However, we do not have a way of determining the triggering mechanism for these old landslides.

 

BRIEF DISCUSSION

As is typical of the landslides induced during the July 16 earthquake, landslides along the Maharlika Highway were mostly shallow. Eighty five percent (85%) of the landslides were 1 meter or less deep (Fig.7a). Seventy-six percent (76%) occurred on 15%-40% slope (Fig 7b).

The earthquake-induced landslides in Baguio City and vicinity are relatively deeper and occurred on relatively steeper slopes compared to the Maharlika Highway landslides. Sixty-six percent (66%) of these were 1 meter or deeper (Fig. 8-A). Fifty-three percent (53%) of the total number of slides here occurred on 25% to 50% or 14° - 27° slope (Fig. 8-B).

 

SUMMARY GRAPH - SLOPE VS. DEPTH

Using the data derived from the inventories of the landslides that occurred along the - Maharlika Highway and Baguio City and vicinity, a generalization can be made. Although the depths of the landslides are within a narrow range i.e. 1 - 3.5 meters, a plot of slope versus depth (Fig.9) indicates that as the slope gets steeper, the landslides gets deeper. This correlation maybe contradictory to some cases of slope failure wherein those occurring on steeper slopes are shallower. This generalization of the 16 July 1990 landslides based on empirical data may be explained if we take a look at the materials involved. The shallow slides involved surficial soil materials. These have minimal cohesion and with the introduction of a destabilizing factor, in this case afforded by intense ground shaking, can be mobilized even on relatively gentle slopes. On the other hand, the relatively deeper slides involved not only soil materials, i.e. surficial and residual, but also bedrock fragments. Considering that the bedrock is overlain by soil horizons, the presence of disaggregated bedrock materials indicate that the line of failure is deep-seated, somewhere between the regolith and the bedrock itself. The inherent cohesion is greater at this zone. This being the case, a more unstable condition is required, in this case, a steeper slope, before the deeper landslides occurred.

 

REFERENCES

Arboleda, R.A., and Punongbayan, R.S. 1991. Landslides induced by the 16 July 1990^ Luzon, Philippines Earthquake. Landslide News.

Keefer, D.K. 1984. Landslides caused by earthquakes, Geological Society of America Bulletin, V.95, p.406-421.

Umbal, J.V. 1990. Report of investigation on the effects of the July 16, 1990 earthquake, PHIVOLCS Internal Report.

Weiczorek, G.F., R. A. Arboleda, and B. S. Tubianosa. 1990. Liquefaction and landsliding from the July 16, 1990, Luzon, Philippines earthquake, Abstract presented at the 1990 AGU Fall meeting.

Ronnie C. Torres*, Ma. Lynn O. Paladio*
Raymundo S. Punongbayan*, and Rosalito A. Alonso**
* Philippine Institute of Volcanology and Seismology - DOST
** National Institute of Geological Sciences - UP

 

ABSTRACT

Liquefaction effects Of the 16 July l990 Earthquake were particularly pronounced in the provinces of Tarlac, Pangasinan, and La Union. These provinces are situated in recent sedimentary environments, four of which exhibited characteristics vulnerability to liquefaction: (1) backswamps in Gerona, Pura, Paniqui and Ramos, Tarlac; (2) river channels and point-bars in Dagupan City, San Carlos and Malasiqui, Pangasinan; (3) sandspits in Agoo and Sto. Tomas in La Union; and (4) deltas in Aringay, La Union and Binmaley and Lingayen, Pangasinan. The liquefaction-affected sediments are all relatively young, water-saturated, moderately-sorted, fine-grained sand deposits. The intense and prolonged ground-shaking during the earthquake caused these sediments to lose strength and subsequently exhibit sand fountaining and lateral Now of the ground. The degree by which an area is affected by liquefaction was largely controlled by intensity and duration of ground-shaking, the character Of the geologic microsettings and the densily of infrastructural development in the area.

 

INTRODUCTION

At 4:26 PM of 16 July 1990, Central Luzon was rocked by the strongest quake to hit northern Philippines this century. The earthquake registered a magnitude 7.8 on the Richter Scale with epicenter at 15.6N and 121.0E near the town of Rizal, Nueva Ecija. A 125 km long ground rupture was consequently formed along the Gabaldon (Nueva Ecija)-Kayapa (Nueva Vizcaya) segment of the Philippine Fault-Digdig Fault system (Fig. 1).

The 1990 Luzon Earthquake was felt in many places at Intensity VIII (based on a modified version of the Rossi-Forel Intensity Scale of I to IX currently used in the Philippines). The partial isoseismal map shown in Fig. 1 gives the limit of felt intensities during the event. However, some modifications may be necessary because there were isolated areas, like Dagupan City, Baguio City and the town of Rizal in Nueva Ecija which seemed to have experienced the earthquake at Intensity IX based on observed wave-like motion of the ground surface (Punongbayan and Torres, 1990) and documented occurrence of thrown-up boulders (Umeda, et al., 1990).

The severe and unusually long groundshaking caused widespread destructions in the form of collapsed manmade structures, liquefaction and associated lateral spreading, and slope failures in places near and far from the ground rupture and epicentral area. Dagupan City and the rest of low lying areas in Central Luzon, which experienced the earthquake at Intensity VIII, suffered largely from liquefaction-related processes.

 

Purpose of the Study

This study aims to achieve the following:

Delineate the areas affected by liquefaction and identify the underlying geological and sedimentological constraints on its occurrence;
Identify the features resulting from or associated with liquefaction.
The result of the study can be used as a basis for land use planning, site-specific infrastructure designs, and further researches on the said Nor related field of studies.
Our study focuses on Dagupan City for a number of reasons. Firstly, Dagupan City is a well-developed population center. Secondly, the phenomenon is of interest not only to geologists, but for engineers as well. The presence of buildings and other infrastructures provides valuable information regarding structural responses to liquefaction. In effect, Dagupan City virtually became a laboratory where theoretical scenarios for liquefaction occurrences were tested against actual geological conditions. Finally, the availability of the record of the city's physical development made it easier to relate damages sustained to the rate of its physical development.

 

Definition of Terms

Liquefaction is a process that transforms the behavior of cohesionless soil from a solid to a liquid (Seed, 1979; Leeder, 1982; Bates and Johnson, 1987). This phenomenon is also referred to as "quick" condition (Leeder,1982). During strong groundshaking, a liquefying body of sediment loses its strength or stiffness and undergoes compaction. The attendant decrease in the volume available for interstitial fluids causes an increase in pore water pressure. Liquefaction occurs when the pore water pressure equals the weight of the overburden.

Liquefaction affects loosely-packed and water-saturated sediments. Its occurrence is influenced by the magnitude of earthquake, ground acceleration, proximity to earthquake generator, duration of shaking, relative density, seismic history and age of the deposit (Seed, 1979; Committee on Earthquake Engineering, 1985; Bennet, 1990). Liquefaction has been observed to be induced by earthquakes with magnitude of at least 5.5 and in areas hundred of kilometers away from the epicenter (Leeder, 1982).

A deposit exhibiting liquefaction undergoes unlimited deformations yielding readily to overlying man-made structures. Severe tilting and subsidence and extensive sand boil occurrences are commonly observed, most noticeably at places with multi-storey concrete structures. Since shear waves are unable to effectively propagate through the liquefied layer, effects of further groundshaking are not very pronounced.

 

Historical Accounts of Liquefaction in Northern and Central Luzon

A review of the history of major disasters in the Philippines (Selga,1926; Repetti, 1946; SEASEE,1985) shows that central and northern Luzon had been repeatedly visited by very destructive earthquakes. In vulnerable areas, such high magnitude earthquakes resulted in liquefaction-related damages. Fig. 2 summarizes the documented occurrences of liquefaction in the Philippines during strong earthquakes. Reference to "sinking" grounds, cracks and outpouring of water and black sand were observed in Dagupan during the 1892 earthquake and are probably analogous to ground subsidence, tension cracks due to lateral spreading and sand boil during the 16 July liquefaction phenomenon.

 

METHODOLOGY

Identification of liquefaction-affected areas and investigation of its impacts of the earthquake began immediately after the 16 July earthquake. The initial investigation was later followed by more intensive surveys conducted to characterize the nature and extent of earthquake damages within the identified areas and to explain why some areas were more severely damaged than others. The surveys involved measurements of the tilt magnitude and direction and the relative subsidence of buildings, and mapping of ground fissure and sand boil distribution.

Relative subsidence was determined by measuring the amount affected buildings had sunk with respect to a reference plane, such as a road surface or sidewalk. In cases when relative subsidence cannot be determined due to the absence of a reference point, high-water marks were measured to provide a minimum estimate of relative subsidence. The measured amounts of relative subsidence, however, would not yield a definite picture on how much ground sinking have taken place as buildings, because of their weight, are expected to sink more and faster than the surrounding land surface. Determination of absolute subsidence requires the reoccupation of geodetic benchmarks and this was not done during the period of the survey.

 

LABORATORY PROCEDURES

Aerial Photograph Interpretation

Geologic interpretation of aerial photographs of Dagupan City taken by the Philippine Air Force three days after the earthquake, together with topographic map interpretation, yielded vital information for the conduct of the study. Two other sets of aerial photographs taken during the period 1926 and 1966-74 provided insights on the rate of physical developments in the city and made possible the identification and delineation of some critical geologic features now obscured by man-made structures.

 

Grain Size Analyses

The study of grain size distribution has some application in predicting the behavior of a sediment body under certain stress condition. The grain characteristics are described by standard statistical parameters. The first of these describes the average size of the sediment grains in a sample. Among the three measures of grain size distribution, mode, median and mean, the latter is considered the most superior estimator (Leader, 1982). Grain sizes are given in millimeters (mm) or phi units where

phi = -log2X

and phi is dimensionless (Matthews, 1982). Table 1 shows the phi value, its equivalent in mm, and the descriptive sedimentary term.

Another parameter is the standard deviation, which is defined as the spread of values about the mean. The significance of this measurements is more appreciated when taken to represent the degree of sorting of the sediments. Liquefaction most often affects sediments that display good sorting.

A third parameter is skewness. It describes the symmetry of the frequency curve. In sedimentology, it shows whether the sample is enriched in finer or coarser sediments as one follows the curve away from the mean (Fig. 3). Table 2 gives a summary of the range of standard deviation and skewness values and the corresponding qualitative description of sorting and fine or coarse-enrichment. Sand bodies susceptible to liquefaction are those that are depleted in sediments finer than 4 phi (.062mm) or mud-sized sediments which can serve to fill existing pores in the framework thereby reducing the amount of water that can be contained in those spaces.

The above parameters can be used to predict the behavior of grains as they accumulate. As deposition continues, the sediments assume a certain packing structure. For equant spheroids, the two extremes in the packing framework continuum are the cubic and rhombohedral packing modes. Packing structure determines many bulk properties of sediments, among these porosity, permeability and stability. Porosity is the measure of fractional spaces between solid particles (Bates and Jackson. 1987). The cubic and rhombohedral packing modes have porosities of 48% and 26% (Fig.4), respectively (Leeder, 1982). The porosity of natural sands with similar packing varies according to sorting (Beard and Weyl in Leader, 1982). Porosity between well-sorted sands and very poorly-sorted sands of the same mean grain size varies by as much as 25% (Leeder, 1982).

Permeability, on the other hand, gives the rate at which fluids stored within pores actually move through the pore system (Bates and Jackson,1987). Porous bodies of sediments are not necessarily permeable. The capacity to allow fluids to pass through arises when the pore spaces within the sedimentary body are interconnected. For sand bodies to liquefy, they must, in the least, be porous.

Stability refers to the capacity to stand any force that tends to deform without destruction of the sedimentary framework (Bates and Jackson, 1987). Sands arranged in the rhombohedral packing mode are more stable because of larger ratio of grain-to-grain contact.

 

PHYSIOGRAPHIC SETTING OF AFFECTED AREAS

Based on the distribution and characteristics of areas affected during the 1990 Luzon Earthquake, four general types of site vulnerable to liquefaction were recognized: (1) back-swamps in Gerona, Pura, Ramos and Paniqui in Tarlac; (2) river channels and point-bars in Dagupan City, San Carlos and Malasiqui, Pangasinan, (3) sandsp its in Agoo and Sto. Tomas, P Union; and (4) deltas in Aringay, La Union and Binmaley and Lingayen, Pangasinan. Although located tens of kilometers away from the epicenter, the damage wrought by the earthquake is many times more severe in these areas than in others nearer the epicenter.

La Union Province

In the province of La Union, liquefaction affected the coastal towns of Sto. Tomas, Agoo and Aringay (Fig 5, Fig.1). These towns form a narrow strip of land at the southern tip of the province and together have a combined area of about 47 km2 along the eastern boundary of the Lingayen Gulf.

The portions of Agoo and Sto. Tomas that suffered the most extensive damages are sitting on a sand spit, with an area of about 9 km2, protruding northwest-southeast into the Lingayen Gulf. A sandspit is a finger-like extension of a beach with one end connected to the mainland, and the other, extending into the open sea. The spit is formed by the accumulation of sand derived from the northern beaches brought in by long shore currents directed southwards into the Gulf. Given a steady supply of sand, the spit grew by building its tip, so that younger and younger sediments are found as one follows the spit into the gulf. Its development can be seen in aerial photographs as traces of sub-parallel beach ridges that lie at oblique angle from the shoreline. Isolated bodies of water similarly disposed, and probably representing old runnels, also give indications of its growth. Fishponds are found between the spit and the mainland.

At Aringay, located north of Agoo, the liquefaction sites were found where Aringay River exits from the mountain just east of the National Road and extends all the way to the coast. Aringay River has built a delta where it empties into the Lingayen Gulf. A delta is a flat tract of land at or near the mouth of a river resulting from the accumulation of sediments supplied by the river. Its name is derived from its triangular outline resembling a Greek letter, Delta (Bates and Jackson, 1987). In contrast to the wave-dominated delta front of Lingayen shoreline, the delta front of Aringay is set in a high energy environment. The high influx of sediments sustained the continuous propagation of the Aringay delta front. Its sediment requirement has been provided by the folded sandstone, shale and silt stone units of the Rosario Formation, a thick sedimentary body that underwent rapid rate of uplift in its latest history (Bureau of Mine and Geosciences, 1982). A fraction of the sediment supplied to the delta front is being redistributed southwards by long shore currents, forming barrier beach sands. Bgy. Alaska, a fish farming village which was extensively affected by sandboils and subsidence, is situated on this barrier beach sand deposit.

Tarlac Province

The Central Plains of Luzon, located between Zambales and Sierra Madre Ranges, is a large sedimentary basin. Thick sequences of sedimentary units grading from deep to shallow marine deposits were encountered in oil drilling explorations in this basin suggesting a history of marine regression. The most recent sedimentary blanket consists of overlapping alluvial plains of several river systems. Dynamic fluvial processes govern the configuration of the Central Plain's present day landforms and ground surface characteristics as evidenced by numerous active and rootless river channels and isolated swamplands.

The areas affected by liquefaction are within the alluvial complex of Agno and Tarlac River systems, such as Paniqui, Ramos, Gerona, and Pura (Fig.6, Fig.1). However, the most extensive damages were sustained by the latter two communities. Agno River emerges from the highlands of Baguio district and courses towards the west. It shares with Tarlac River a confluence point from where Agno River deflects to the north towards Pangasinan and empties into the Lingayen Gulf. Channel avulsions along Agno River, the most recent of which occurred in the vicinity of Urbiztondo, and isolated backswamps, such as those found in Pura, are the relics of the earlier subenvironments associated with the former active channels. These abandoned channels and backswamps comprise the patches of swamplands in Tarlac and Pangasinan. Groundwater well drilling in Pura revealed a fining upward sequence of medium to fine sand overlain by less than a meter thick silt to clay layer, indicating deposition in a low-energy environments with periodic influx of sediments. This condition is true in a backswamp environment that is repeatedly inundated during extreme precipitation in the watershed area. Much of the sediments supplied by the Tarlac River has come from eruptions of Mount Pinatubo.

Dagupan City

Dagupan City is located on the northern part of Pangasinan and along the southern shores of Lingayen Gulf. It has a total land area of 37 km . It lies just a meter above sea level and is traversed by Pantal River, a major distributary of the Agno River.

Macro-setting: Wave-dominated delta

Dagupan City is situated at the eastern margin of the delta of Agno River. The present active channel of Agno River traverses the western boundary of Pangasinan and empties into Lingayen Gulf. Channel avulsion in the vicinity of Urbiztondo consists of a river course flowing along the east side of San Carlos City and towards Binmaley (Fig.7).

Although a high energy environment prevails along the shores of Lingayen Gulf, the delta front of Agno River continues to prograde slowly due apparently to the confinement of sediment redistribution within the Lingayen-Dagupan shoreline. Delta front progradation is maintained in this environment probably through barrier-beach accretion. Strong wave action redistributes most of the sediments supplied to the delta front by Agno River and its distributaries to form multiple elongate coastal ridges aligned parallel to the Lingayen Dagupan shoreline. Discrete groups or bundles of parallel coastal ridges separated by discontinuities indicating the changes in channel positions (Psuty, 1967) may exist within a A: delta, with the bundles occurring in pairs and are symmetrically disposed with respect to the active emptying points of distributary channels. Thus, beneath Dagupan City, these bundles of coastal ridges are very likely to be found.

Micro-setting: Meandering river environment:

The meandering Pantal River flows through Dagupan City and reworks the marine deposits of the Agno River delta. Its sediment supply comes from reworked volcanic materials of Quaternary volcanic cones dotting the southeastern plains of Pangasinan and of Mount Pinatubo in Central Luzon, and from detrital materials brought down by Agno Rives from the highlands of Nueva Vizcaya and Benguet. The high inflow of sediments frog these sources into Pantal River, especially during flood stages, induces increased fluvial sedimentation at places where there exist recently abandoned coastal ridges, as in the vicinity of Dagupan City. Consequently, fluvial deposits can be seen either partly or wholly covering these abandoned coastal ridges along the course of Pantal River. Formation of levees F attests to the high sediment supply of Pantal and high frequency of flooding in the study area.

The dynamic lateral shifting of Pantal River in the recent past gave rise to its meandering pattern. It left numerous abandoned channels and created a low-lying terrain made up of levees and backswamps (Fig.8). Many of these backswamps and other depressed grounds found within Dagupan City become inundated during floods and high tides.

 

RESULTS OF STUDY
Effects of Liquefaction

In contrast to other areas devastated by the earthquake, Dagupan City sustained only a few collapsed structures due to ground shaking The effects of groundshaking were limited to the damaged unreinforced old Catholic and Protestant church buildings. Most of the destructions noted in the city were attributed to liquefaction triggered by an estimated peak ground acceleration of 0.18g (Midorikawa, 1990). Observable effects of liquefaction include sand boil, lateral spreading, land subsidence and upheaval, and ground undulation and fissuring. The commercial district, located west of Pantal River and between A.B. Fcrnandez Ave. and Perez Blvd., was severely damaged. Residential houses in Pogo Chico, Pogo Grande and Lasip Grande (Fig.9) were partially to totally damaged. At Pogo Grande, some mango trees were uprooted. The blocks enclosed by Gomez, Burgos and Zamora streets, which contain the old and new Catholic Church buildings and the town plaza, were largely unaffected (Fig. 10). :

Although comparable in area to that of Dagupan City, the magnitude of damage due to liquefaction in the towns of La Union, together with those of Tarlac, appears less serious,the effects being confined to less populated and less developed community centers, and to fishpond areas. In general, however, where multi- storey buildings stood, these sustained t moderate to heavy damage.

Liquefaction produced sandboils, relative ground settlement, and lateral spreading affecting houses and utilities, water wells, roads and irrigation ditches. As a result, buildings were tilted, floors and pavements were ripped-off, and fishponds were filled with sand. In some areas, settlement of buildings resulted in temporary flooding of their immediate surrounding.

Sandboils are the most commonly recognized evidence for the phenomenon. Witnesses observed sand and water fountains a meter high or even greater, while sandboil diameters ranged from a few centimeters to in excess of 6 meters. At Sitio Cabaroan, Sto. Tomas located at the southernmost end of the spit, a resident recalled that sandboils formed in rows parallel to the shoreline thus indicating the most recent and consequently, the least consolidated deposits in the area. Ground fissures were found perpendicularly disposed from the sandboils. Furthermore, high tide now encroaches the area resulting in a 0.4 meter high flood level. Relative ground subsidence amounted to as much as 1.5 meters. Damage to unreinforced buildings was moderate to heavy and consist of vertical and horizontal cracks on walls, uneven or ripped-off floors and pavements, tilting and subsidence.

During the Loma Prieta earthquake of 1989 in California, damage caused by liquefaction was primarily due to large horizontal and vertical displacements of the ground (Plafker and Galloway, 1990). The liquefied layer flowed even on very gentle slopes. Moreover, the ground on top of the flowing layer broke into small slabs that settled relative to each other.

 

GRAIN SIZE ANALYSES

Agoo Samples

The samples have mean grain size between 0.105 to 0.210 mm (2.43 phi and 3.05 phi) (Fig. 11). These are described as fine to very fine sands and they display moderate to moderately-well sorting. The fine-grained character of the samples reflects the amount of transport the sediments have undergone. Since the sediments of the spit are derived from the north, it can be expected that sands from the north are coarser. As the sediments are transported, they are continually being winnowed, the coarser materials being dumped near the source while the finer sediments are transported farther. Most beach deposits display good sorting because of their continuous exposure to wave action.

Pura Samples

The mean grain-size of the samples (Fig. 11) is between 0.177 to 0.074 mm (2.65 phi . and 3.72 phi) and are fine to very fine-grained sands. They are moderately to moderately well sorted. Looking at the graphs, one can readily recognize a difference in the overall grain l l characteristics of the samples from Pura compared to those of other areas. First, the fined mean grain sizes are represented by this group of samples. Second, the general behavior of each sample, as seen from the frequency curves, is not comparable to one another. PSB-1 is enriched in sediments finer than sands. For PSB-2, the curve exhibits two grain size ranges of almost equal importance. Of the three, PSB-3 shows characteristics most comparable to the samples from other areas. In all cases, the curve shows depletion of sediments coarser than 3 phi and a corresponding dominance of finer sediments.

The behavior of the Pura samples can be explained in terms of different sub environments, each with different characteristic deposits, existing across the alluvial plain. As the river migrates laterally, so does the sub environments, and older deposit of one sub environment become juxtaposed to or overlain by deposits of the most recent regime. The tendency of the samples towards fine enrichment probably reflects backswamp environment where stagnant waters allowed fine sediments to settle and be deposited.

Dagupan Samples

The sand boil samples from Dagupan have mean grain-size between 0.250 - 0.125 mm (2.14 phi and 2.80 phi) (Fig. 12). They, therefore, fall within the range of fine sands. They are moderate to moderately well sorted. Most of the samples have a tail towards the coarser-grained end.

Certain areas around Dagupan City are built on meander scars that naturally fill as fluvial processes proceed. The filling materials consist of fine-grained sediments deposited by Pantal River. Other areas represent backfill sites where the filling materials were derived from beach deposits, sands that have been transported and winnowed by wave action. In both cases, the sediments have been sorted to varying degrees by the different processes active in their respective environments of deposition, thus making them susceptible to liquefaction.

 

DAGUPAN CITY : A Case Study

Physical Development of Dagupan City

Spanish writers described Dagupan as an extensive marshland with rich alluvial soil. It was thickly covered with mangrove and nipa palm trees which served as habitat to many marshland wildlife species. Early settlers lived in small clusters of houses along the shoreline and river banks of Calmay, Pantal, and Bonuan. Later migrants moved inland occupying the agricultural lands of Malaued, Lasip, Pogo, and Bacayao. Pantal and Bonuan became the fishing, salt-making, and "bangus" (milkfish)raising centers and Malaued, the agricultural settlement area. Travel was mainly by "bancas" (dugout canoes) and sailboats through the river channels.

In 1590, the house clusters were resettled into compact communities and converted into a town named initially as Bacnotan and renamed later in 1720 as Dagupan. A site for the town plaza was constructed along Pantal River surrounded by the town hall in the east public market in the north, and the Catholic Church in the west (Pangasinan Folio, 1970 In 1780, Pantal, originally named Pantalan (port), became a trading center and docking station for merchant ships. At about the same time, bangus industry thrived and more mangrove swamps were converted into fishponds. The development of Dagupan as a commercial center was firmly established in 1891 when the Manila-Dagupan railway was completed. Up to the 1900's the site of the present public market was still a swamp with waist deep water. Much of the present downtown area along A. B. Fernandez Ave. (formerly Torres Bugallon Avenue) was a marsh. Travel by boat along the Agno River was still the most practical means of transport. In 1908, the commercial center extended beyond the Quintos Bridge on the other side of Pantal River. The continuous growth of the city necessitated the construction of Perez Blvd. and Magsaysay Bridge in 1948 to create more space for commercial activities through the usual practice of reclaiming and construction on swamplands and less productive fishponds.

Fluvial Sedimentation and Artificial Channel Cut-offs

The active shifting of Pantal River left a belt of abandoned meanders alongside it. The positions of the old meanders are indicated by the looping configuration of swampy areas and other natural drainages (Fig. 16). These are also prominent and, therefore, easily identifiable in aerial photographs. The age relationship of an abandoned meander to the active channel could be inferred from its depth, distance from the present active channel and, where several meanders intertwined, cross-cutting relationships.

Most of the meander scars exhibit well-developed point bar deposits and scroll bar ridges. However, some point bars are already obliterated by cross-cutting meander loops and are covered by levee deposits. A peculiar characteristic of very young active meanders, particularly those within the vicinity of the city proper, is the absence of distinct levees. Based on this, it is very likely that some of these channels have been artificially made, probably during the development of the city.

Channel abandonment along Pantal River also resulted from construction of artificial cut-offs. Slow sedimentation of suspended materials and episodic influx of flood-borne sediments eventually filled up the abandoned channels. These natural reclamation materials are largely uncompacted and water-saturated sediments and, as such, highly susceptible to amplified ground shaking and liquefaction. At some later stages of natural reclamation, the abandoned channels are transformed from oxbow lakes into swamps or marshlands.

Artificial cut-off and reclamation have long been employed along Agno River for two primary reasons: (1) to shorten travel time around meander loop and (2) to diffuse floodwater especially at constricted portions. One exceptional case was the famed Limahong Channel, named after the Chinese pirate who established his colony in Lingayen during the 1600s. According to historical accounts, the combined Filipino and Spanish forces laid siege on his fortress by blocking the river outlets. Limahong broke through the siege by sects digging a channel from the Agno River to Lingayen Gulf (Callanta, 1989)

An indication of man-made alteration on the fluvial environment of Dagupan City isle abrupt changes in the sinuosity of Pantal River. Based on the ratio of channel length and meander wavelength, the sinuosity of the active and abandoned channels of Pantal Rid, lying south of Dagupan City proper has an average ratio value of 2.31 and 4.19, respectively. In contrast, the meander character around the city proper was calculated at 1.40 formula} active channel and 2.14 for the abandoned channels. These sinuosity measurements distinguish straight and meandering channels at boundary ratio of 1.5. Therefore, the channel character of Pantal as it approaches the City proper transforms from a meandering channel to a straight channel. Furthermore, the similarity of the sinuosity of the abandoned channels passing through the city and the active meanders at the southern continuity of the river suggests that these abandoned meander were not yet primed for natural cut-off but were artificially severed from the main channel.

The effects of the 16 July 1990 Earthquake

Sand boils were the most extensive effects of liquefaction in Dagupan City. During the earthquake, sand boils were erupted through cracks at the sides of buildings, ruptured pavements, and covered concrete roads with dark gray fine sands and muddy waters. Drainage systems were clogged by the accumulated sand causing temporary flooding of the main thorough fares.

Sand boil distribution in Dagupan City, as delineated from aerial photographs taken three days after the earthquake and from field investigation, is shown in Fig. 13. Based on standard penetration test data of the Department of Public Works and Highways, the liquefiable layers are up to about 5m below the ground surface. In some places, however, these are shallow enough to be directly observed through open fissures. For example, the deposit found inside the Divine Word Academy adjacent to Nazareth Hospital along Rizal Extension (Fig 10) appears to have originated from a layer less than a meter below the ground surface.

Lateral spreading accounted for most of the destruction of swampy areas in Dagupan City. Buildings and other manmade structures were damaged when river banks slid into Pantal River and dry lands into the swampy areas during the earthquake.

Lateral spreading along Pantal River appears to be confined to constricted portions of the stream channel. Magsaysay Bridge is located across one of these constrictions and its collapse was brought about by lateral spreading on both sides of Pantal River (Plate 1). During active lateral spreading of opposing banks of Pantal River where Magsaysay Bridge abutted, the local compression generated was directed towards the bridge, and it swept away the piers at the same time when the riverbed was liquefying. As a consequence, the bridge , was broken into several segments like an accordion, although the portion close to the west abutment collapsed horizontally onto the riverbed. The segment abutting against the bank was thrust westward under the adjacent segment and the middle pier underwent subsidence and tilting towards the east. A similar compressional phenomenon was observed where a portion of Galvan St. overlying an open canal was thrust over a resisting abutment.

Ground subsidence is a direct consequence of liquefaction. However, the amount of subsidence in areas affected by liquefaction can only be determined relatively due to the absence of an undisturbed or fixed reference point. In general, places where buildings stood subsided relative to the streets, and understandably so. Subsidence phenomena are notable within the commercial district where some buildings sank by as much as 2 meters (Fig.14).In general, most of the affected buildings in Dagupan City subsided by less than a meter.Adjacent concrete pavements dip towards the subsided structures and ground cracks are disposed perpendicular to the direction of subsidence. The resulting subsidence in Dagupan City becomes more evident when the affected areas got flooded by rainwater, high tide in cursion and, jetted-up groundwater. Flooding was aggravated by the disruption and clogging of both the natural and man-made drainage systems. Some houses remained underwater by 30-50 cms. for several months. The whole stretch of Don Jose Calimlim St. and swampy areas and fishpond communities, such as Bgy. Lasip Grande, remained underwater even during low tide conditions.

In a more severe form of liquefaction, differential subsidence is usually associated will the tilting of heavy structures. Severely tilted buildings are concentrated along Perez Blvd. One is tilted by as much as 19 degrees (Plate II), but generally, the magnitude of tilt is within 2-5 degrees (Fig. 15).

Buried buoyant structures such as gasoline storage tanks (Plate III), septic tanks, and drainage pipes exerted upward pressure resulting in the upheaval of the ground and breaking of pavements, thus affecting the operation of some gasoline stations. Liquefaction also caused water supply problems, especially the availability of potable water many weeks after the earthquake.

Ground undulation is another feature associated with liquefaction. An eyewitness observed that the ground appeared to roll during the earthquake. He described a jeep parked along the road appeared and vanished from his line of sight. Evidence of rolling ground seems to have been preserved in the deformation of some fences and roads (Plate IV).Along the portion of Dagupan-Lingayen road enclosed by Tapuao-Malued diversion road, cracks developed in a concrete fence coincide with the crests and troughs of ground undulation wavelength. The cracks which formed at the crests are characteristically open and tapering downwards - an extensional feature - and the ones that formed at the trough exhibit shortening feature in the form of tight fractures. Using this observation as basis for determining the wavelength of ground undulation, the amount of separation between the extensional and the shortening cracks was measured along a deformed residential fence and a ground undulation wavelength of about 25 meters was obtained. Observable effects of ground undulation did not extend beyond the junction of the Tapuac-Milued and the Dagupan-Lingayen roads.

Correlation of Fluvial Sedimentation and Distribution of Damage

Liquefaction damage and the distribution of affected areas in Dagupan City appear to have strong geological controls. The extensive earthquake-induced secondary ground a failure in Dagupan City is confined mostly to built-up areas on recently abandoned river meanders, banks of active channels, and relatively young point bars. Structures constructed outside of these young geologic features suffered little or no damage during the earthquake. Conversely, it is also to be expected that areas with extensive occurrences of a sand boils and those with heavily tilted and subsided buildings should be where these geologic features are to be found. The margins of abandoned river channels thus serve to demarcate the boundaries between areas with totally damaged buildings and those with partially to undamaged ones. The liquefaction-prone layer would most probably correspond to the deposits in the abandoned channels and point-bars and would have a thickness of about 5-6 meters, which is approximately equal to the depth of Pantal River.

Liquefied deposits tend to flow towards open and recently reclaimed river channels. When this happened in Dagupan City during the earthquake, multi-storey buildings and residential houses on the liquefied point-bar deposits tilted away from the open and recently reclaimed river channel and in a direction opposite to that of lateral spreading.

Varying degrees of damage were sustained in the different affected areas of Dagupan City. For instance, the area around Perez Blvd., which is located in a readily recognized meander scar and well-developed point-bar, sustained more damages than the area around Tapuac-Malued road, which is an older meander belt. Similar liquefaction effects in the vicinity of Perez Blvd. can be observed in Pogo Grande, but these effects are at a subdued level because only residential houses are found here. Pogo Grande is also situated in a young meander scar of about the same age as that around Perez Blvd. All these observations clearly indicate that susceptibility to liquefaction and the attending degree of damage to structures within the different parts of Dagupan City can be related to the relative ages of the geologic features they occupy and therefore, by the relative ages of deposits underlying them. In general, sandy deposits in relatively old meander scars are less prone to liquefy than those found in recently abandoned channels and when they do liquefy, damage to structures built on them would only be of limited extent.

The degree of destruction along A.B. Fernandez Ave., which largely lies on a reclaimed swampland, is generally less than that in the Perez Blvd. area except near its intersection with Rizal St. where there occurred pronounced relative subsidence and structural tilt. The heightened effect of liquefaction along a 100m stretch of A.B. Fernandez Ave. can be traced to modification of the channel of Pantal River. Prior to north eastward expansion of Dagupan City, Pantal River used to meander around the area now partly occupied by A.B. Fernandez Ave. and Rizal St. before running parallel to Pantal Road (Figs 16). Thus, the segment of A.B. Fernandez exhibiting severe liquefaction related damages coincides with the crossed-over area of the old Pantal River. It is here underlain by young deposits of similar age as those in the Perez Blvd. area. The rest of A.B. Fernandez Ave. that was built on a reclaimed swampland suffered less damage through liquefaction because it is basically underlain by relatively older and better compacted deposits.

 

SUMMARY AND CONCLUSION
The study revealed that the effects of liquefaction during the 16 July 1990 event were experienced in areas both far and near the epicenter of the earthquake. These areas are built on different sedimentary environments: deltaic for Dagupan City and Aringay, sandspit for Sto. Tomas and Agoo, and alluvial plain for the affected areas in Tarlac. However, results of the grain size analyses showed a striking similarity in the characteristics of the sandboil samples from the different environments. In summary, they have mean grain size consisting of fine to very fine sands and show a preferred depletion in sediments finer than sand size. They exhibit a moderate degree of sorting, thus fulfilling one of the very first requirement for liquefaction.

In terms of water saturation, all of the recognized environments where liquefaction occurred have access to an abundant supply of water: the river for Dagupan and Aringay, the sea for Sto. Tomas and Agoo, and the swamps for those areas in Tarlac. The level of vulnerability to liquefaction hazards of the various areas can be assessed by determining their location in relation to ancient and recent abandoned river channels, and to recent beach zone features. The study has pointed out that built-up areas on abandoned river channels, at the banks of the active river channel and on young point bar deposits are most vulnerable to liquefaction hazards. This relationship is most clearly demonstrated in Dagupan City where the spatial distribution of damages points to the fact that the line separating the damage and undamaged areas is a geological boundary.

In general, areas vulnerable to liquefaction can be summarily identified from their physiographic situation . Detailed delineation of these areas may be further achieved by using standard engineering techniques.

The liquefaction phenomena associated with the 16 July 1990 earthquake is not a new experience in the Philippines. Historical records show such events happening across the country since the Spanish era, environments associated with liquefaction has been recognized by earlier researchers also in connection with Philippine earthquakes. However, the magnitude of damage brought about by this recent event calls attention to the fact that indepth studies still have to be made with regards to recognition of other environments prone to the phenomena. Along with these studies, an inventory of such areas must also be conducted both in general and in detail.

 

RECOMMENDATIONS

This study has shown that several steps may be undertaken to minimize the effects of liquefaction. One would be to avoid known liquefaction-prone areas. In cases where such places are to developed, knowledge of the physical properties of underlying materials must be studied in order to use the proper engineering techniques needed to minimize the effects of liquefaction.

With regards to the reconstruction and future expansion of those areas affected by liquefaction during the 16 July 1991 earthquake, it must be realized that this phenomena may happen again. Since it is not practical to relocate these communities, it becomes imperative to consider their unique geological environment and high vulnerability to liquefaction hazards. Various structural works to be done within these areas must be properly designed and made compatible with the existing geological conditions. Detailed geologic and foun dation studies will have to be conducted to delineate the boundaries of areas which are likely to liquefy during the next earthquakes. Results of studies such as this, should be shared and discussed with the public and potential land users for the purpose of minimizing losses from future major earthquakes. More importantly, policy makers will be able to maximize the land-use potential of these areas and, at the same time, minimize the risks involved during any future earthquake events.

 

ACKNOWLEDGMENT
This study is supported in part by the Department of Environment and Natural Resources. We deeply appreciate the kind assistance extended to us by Secretary Fulgencio S. Factoran of the said Department by providing the invaluable sets of aerial photograph coverage of Dagupan City; by Dr. Kelvin S. Rodolfo of the university of Illinois at Chicago for his technical support; by Dr. Emmanuel V. Tamesis and Jesse V. Umbal for reviewing the preliminary draft of the paper; by the staff of the Dagupan City Engineers Office for providing the maps and data pertinent to the conduct of the study and to the City Planning and Development Office for letting us copy the 1966-74 sets of aerial photographs of Dagupan; by our colleagues at the Institute.

 

REFERENCES

Bates, R. L. and Jackson,J. A., eds. (1987). Glossary of Geology. 3rd ed. Virginia: American Geological Institute.

Bennet, M.J. 1990. Ground deformation and liquefaction of soil in the Marina District. In Effects of the Loma Prieta Earthquake on the Marina District, San Francisco, California. USGS Open File Report No. 90-253. Menlo Park. Dl-36.

Allanta, C. V.1989. The Limahong Invasion. Quezon City, New Day Publishers.

Committee on Earthquake Engineering. 1985. Liquefaction of Soils During Earthquakes. Commission on Engineering and Technical Systems, National Research Council. Washington D.C.: National Press Academy. 240 p.

Seeder, M.R.1982. Sedimentology. London: George Allen and Unwin. 344 p.

Maso, M.S. and Smith, W;D.1913. The Relation of Seismic Disturbances in the Philippines to the Geologic Structure. Phil. Journ. Sci. 199-233.

MatthewS, R. K. 1984. Dynamic Stratigraphy. 2nd ed. New Jersey: Prentice Hall, Inc. 489 P

Miall, A.D. 1981. Analysis of Fluvial Depositional Systems. Paper presented at the AAPG Fall Education Conference. Calgary. 75 p.

Midorikawa, S.1990. Ground motions and site conditions in affected area by the Luzon, Philippines Earthquake of July 16, 1990. Tokyo Institute of Technology. (n.p.)

Pangasinan Folio.1970. Historical Document. I Lingayen. H.G. Henarez and Sons, Inc.

Plafker, G. and Galloway, J.P., eds. 1990. Lessors learned from the Loma Prieta, California, earthquake of October 17, 1989. USGS Circular 1045. Washington: United States Government Printing Office. 48 p.

Psuty, N.P.1967. The geomorphology of beach ridges in Tabasco, Mexico. Louisiana State Univ. Coast. Stud. Ser., 18, p .51. in READING, H.G., ed. (1978). Sedimentary Environment and Facies. London: Blackwell Saientific Publications.

Punongbayan, R. S. and Torres, R.C. 1990. Correlation of river channel reclamation and liquefaction damage of the 16 July 1990 Luzon earthquake in Dagupan City, Philippines. 15 p.

Rantucci, G.1996. Preliminary Report on the Sand Liquefaction induced by the 16 July 1990 Earthquake in Dagupan City, Pangasinan, Philippines. Paper presented during the 3rd Annual Geological Convention held at the UP-NIGS, Diliman, Q.C. 7 December 1991.

Repetti, W.C. 1946. Catalogue of Philippine earthquakes, 1589-1899. Bull. of the Seismological Soc. of America. 36: 133- 322.

Riley, M.C. 1953. A new roundness scale for sedimentary particles. J. Sed. Petrol. 23: 117-119.

Seed, H. B. 1979. Soil liquefaction and cyclic mobility evaluation for level ground during earthquake. Journal of the Geotechnical Engineering Division 105/GT2, 210-255

Selga, M.P. 1926. Philippine Earthquakes. Weather Bureau Seismological Bull. for 1926. Manila. 67-103.

Southeast Asia Association of Seismology and Earthquake Engineering (SEASEE).1985. Series on Seismology. (]985-86) IV: Philippines. E.P. Arnold (ed.)Washington D.C.: Government Printing Office.

Torres, R.C., et al. 1990. Fluvial meander sedimentation as a locus determinant for liquefaction damage in Dagupan City, Pangasinan. Paper presented at the Geological Society of the Philippines' 3rd Annual Geological Convention held at UP-NIGS, Diliman, Q.C. 7 December 1991.

Umeda, Y., et al. 1990. The thrown-up boulders by the 1990 Philippine Earthquake. Unpublished report. Disaster Preparedness Research Institute, Kyoto University.

MAPS

Hydrographic Survey of Portions along Pantal-Bacayao-Tulao Rivers, Dagupan City. (n.d.) Dagupan City Engineer's Office.

Bartolome C.Bautista, Ma. Leonila P.Bautista, Anel R. Rasdas
Angelito G. Lanuza, Erlinda Q. Amin and Perla J. Delos Reyes
Philippine Institute of Volcanology and Seismology - DOST

 

ABSTRACT
The 16 July 1990 Luzon earthquake severely affected areas which were several tens of kilometers away from the ground rupture or earthquake epicenter. These were Baguio, Agoo and Dagupan City.
To determine aftershock pattern and to understand why heavy damages were incurred by these areas, PHIVOLCS closely monitored the ensuing aftershock activity by operating temporary seismic stations in strategically located sites around the aftershock area, in addition to its existing seismic stations.
Aftershocks lie along the ground rupture zone and around the Baguio and Agoo areas. The aftershocks pattern and the distribution of heavy damages and impacts to environment suggest the possibility that two sequences of faulting might have occurred: along a main fault, the Philippine Fault-Digdig Fault system located at Nueva Ecija and Nueva Vizcaya provinces and an E-W oriented subfault close to Baguio clip and Agoo. Aside from factors like topographic effect, differential site response and seismic wave radiation pattern, the movement of the said subfault could have contributed to the extensive damage in Baguio City.
Focal mechanism data of strong aftershocks as published by the National Earthquake Information Center (NEIC) were plotted on map and section to evaluate the possible sense of movement and orientation of stress fields. The dominant mechanism of strong aftershocks occurring in the Baguio area indicates an extensional type of faulting which is in agreement with the sense of left-lateral movement of the main fault.

 

INTRODUCTION
The 16 July 1990 earthquake was the biggest earthquake too occur in the Philippines since 1976 and in Northern Luzon for the last century. Its negative impacts were so widespread and devastating that it brought to the fore the necessity to reassess and re-evaluate the effectivity of the existing disaster preparedness plans and programs of the government.
This study was sponsored by the Department of Environment and Natural Resources under the Documentation and Data Base Establishment of the July 16, 1990 Earthquake Program. For this particular study, we aim to achieve the following:
      a. To present a summary of seismological information about the 16 July 1990 earthquake based on data from PHIVOLCS seismic network, and from short-term temporary seismic investigations by both PHIVOLCS and international groups of scientists.
        b. Using seismological approaches, to explain why very extensive areas were devastated by the 16 July 1990 earthquake.
         c. To present significant pre-earthquake observations which could be used as precursor for future earthquakes.

The Philippine Fault - the Culprit
The earthquake was triggered by the sudden movement of the northwest segment of Philippine Fault Zone (PFZ) and of its north trending splay, Digdig Fault. The PFZ is an active fault system which can be traced from Mindanao in south eastern Philippines, going north west and passing through the islands of Leyte, Masbate, Ticao Island, Bondoc Peninsula, Dingalan to Lingayen, Pangasinan (Figure 1). Based on geologic data, the age of the 1200-km long fault is estimated as Pliocene (Barrieret et.al., 1991). The latest pre-1990 movement of this fault occurred on, 17 March 1973 at Ragay Gulf in Quezon Province. That earthquake, with Ms of 7.5, resulted to horizontal displacements of 1.1 to 3.4 meters.
Along the rupture with no evident vertical component (Morante, 1974). From 1500 to 1983 at least 25 strong earthquakes (Figure 2) could be correlated to the movement of PFZ (Punongbayan and Umbal, 1990).
The most obvious geomorphological evidence of its recent movements could be found in Leyte in a series of offset streams and fault scarps. Other geomorphic features have been observed from field observations, satellite imagery, aerial photographs and seismic profiles (Barrier, et.al., 1991). According to Barrier et.al. (1991), there are two main segments the Philippine Fault - central section from Bondoc peninsula to Mindanao and the northern segment. The central segment is purely left-lateral strike-slip based on kinematic indicators while the northern segment has a thrust component.

 

TECTONIC SETTING
The susceptibility of the Philippines to strong earthquakes can be explained by its tectonic setting. The country is sandwiched between two opposing plates – the South China Sea Plate and the Philippine Sea Plate. The PFZ formed as an adjustment to continuous opposite subductions. This is supported by the agreement in values of slip notes of the two plates and the rate of motion of the PFZ using seismic moments of past earthquakes whic occurred along the fault (Acharya, 1980).

 

HISTORICAL AND RECENT EARTHQUAKES
From the review of accounts of historical earthquakes by Repetti (1946), at least one event could be correlated to possible movement of the same fault segment. This occurred in 1645 and was said to have destroyed Manila and was heavily felt in the hinterlands of Gapan. It is strongly suspected that the epicenter of this event is similar to the 16 July 1990 earthquake. However, due to uncertainties common to such historical accounts, we leave ourselves open to all probabilities with regards to prior earthquakes which occurred in the epicentral area until future trenching activity could determine earthquake recurrence in the segment. In terms of available instrumental data from 1900 to 1988 and except for the 1645 earthquake, the general area where the 16 July 1990 earthquake occurred has been virtually free from any destructive events in the past (Figure 2).

 

SEISMIC NETWORK
The agency mandated by the Philippine government to monitor and study earthquake occurrences in the country is the Philippine Institute of Volcanology and Seismology (PHIVOLCS). This assignment is a fresh mandate after PHIVOLCS' reorganization in 1984. Prior to that, seismological observations were the responsibilities of another government agency, the Philippine Atmospheric, Geophysical, Astronomical Services Administration (PAGASA).
There were 14 operating manned seismic stations during the occurrence of the 16 July 1990 earthquake (Figure 3). The nearest station to the epicenter are the seismic stations at the Central Office in Quezon City and Baguio City. Ensuing aftershocks caused power failure in Baguio City which also temporarily caused stoppage of operation of the seismic equipment in the station.
The seismic stations of PHIVOLCS are equipped with short-period seismographs and are manned by well-trained field personnel on a 24-hour basis. Daily earthquake data are transmitted every morning to the Central Office in Quezon City for processing, interpretation and dissemination. The field personnel are also required to report to the Central office seismic data of felt events or those with magnitudes 4 and above immediately after their ocurrence. Earthquake parameters are determined with the use of computerized hypocentral determination program utilizing a damped least square algorithm and a velocity model adapted from Jeffrey and Bullen. It requires a minimum of five P-arrival data and if possible one good S-arrival. Results are considered good when the root mean square (rms) is less than 1, with minimal number of iterations and after undergoing iteration for every one km. Accuracy of plottings are in the order of +/- 5-15 kms. For magnitude calculation, a Quick Basic program MAGCAL2utilizes formula developed by Uy and Punsalan (1985) for Philippine earthquakes. The data required are time duration and distance, in degrees, of the epicenter to the recording stations. Results arc displayed in local magnitude (Ml), surface magnitude (Ms) and body magnitude (Mb). For magnitude determination, calculations are based on data from well-calibrated PHIVOLCS seismographs already located in predetermined seismic stations.

 

QUICK RESPONSE TEAMS
The first quick response team dispatched was a team composed of available geologists and seismologists who went around Metro Manila in the late afternoon of 16 July 1990 to conduct initial ocular observations of buildings in the city.
The next day, two teams equipped with portable analog seismographs left for Cabanatuan City, Nueva Ecija and to Dagupan City, Pangasinan. They installed the first two temporary PHIVOLCS seismic stations in Cabanatuan (CAB) and Dagupan (DAG) Cities. Aside from seismic observations, they also did damage assessments, documented impacts and acted as public educators. Data from these two initial seismic stations (CAB and DAG) helped a lot in plotting most of the initial aftershocks. However, these temporary stations were later transferred to Bolinao (BOL), Pangasinan, Bontok (BON), Mt. Province and Pantabangan (PEP), Nueva Ecija (Figure 4).
Being an international concern, the international geoscientific community sent several Maps to conduct aftershock monitoring and studies. PHIVOLCS seismologists and scientists from the U.S. Geological Survey (USGS) installed four GEOS seismic instruments in Rizal, Nueva Ecija and another set in Baguio for several days in August 1990. In Baguio City, they installed these inside the collapsed Hyatt Terraces Hotel and later, at the Export Processing Zone Authority (EPZA) buildings, where two EPZA buildings of similar designs and structures located in different sites were shaken differently due to differential site response during the earthquake.
The Disaster Prevention Research Institute (DPRI), Kyoto University also conducted two series of aftershock observations: from 30 August to 04 September 1990 and another from 17 November to 07 December 1990, using EDR-1000 digital seismic equipment.

 

STRONG MOTION DATA
Four strong motion instruments were in operation during the earthquake. These were located inside the compound of the Philippine Nuclear Power Plant (PNPP- 1), located about 150 kms from the quake's epicenter. These were being operated and maintained by the National Power Corporation (NPC). The highest value from among the peak ground acceleration values obtained from strong motion instruments of NPC was 44 gals or 0.04 g (National Power Corporation Internal Report No. EDS-90- 108 dated 18 July 1990) which corresponds to Intensity VI in the adapted Rossi-Forel Intensity Scale of I-IX (Table 1). The spectrum of ground motion from two of the triggered instruments is shown in Table 2 while these data are presented in graphical form in Figures 5 and 6. The isoseismal map (Figure 7) which was drawn based on extent of damages, macroseismic reports from PHIVOLCS seismic stations and results of interviews agree with the results of available strong motion data. Likewise, based on available information, there were no strong motion data in other parts of the affected areas.

 

THE MAIN SHOCK

Hypocentral Location and Magnitude of the 16 July 1990 earthquake
The results of the hypocentral determination using data from the PHIVOLCS network is shown in Table 3. There are eight reliable P-arrival time data from eight permanent stations. As shown in the table, the earthquake's epicenter was located using six P-readings at 15.714 N., 121.156 E. with depth of 12.67 kms +/- 6.33 kms. The origin time was 07:36:35.35 (GMT). Meanwhile, using information from 325 international stations including those of PHIVOLCS', the National Earthquake Information Center (NEIC) of the U.S Geological Survey placed the epicenter at 15.679 N.,121.172 E. with depth of 25 kms. The + sign in Figure 8 shows the location of PHIVOLCS epicentral determination while the open circle shows the NEIC plot. The degree of error for each plot are represented by the length of the cross and the radius of the circle.
All of the seismic records from the operating stations clipped or saturated and no reliable amplitude measurements were available to serve as basis for magnitude determination. However, with the use of an empirical formulae by Uy and Punsalan (1985), coda length of the records from different local stations, PHIVOLCS estimated an average duration magnitude of around 7.2. With the use of surface wave amplitude from distant stations, the NEIC estimated the surface magnitude to be around 7.8. The Japan Meteorological Agency (JMA) using records from Japanese network estimated a Ms of 7.6.

The Rupture Process
Faults that generate large magnitude earthquakes usually do not break in one single movement but in a series of small movements. This is due to the inhomogeneity of the rocks along the fault plane. Irregularities along the fault can also cause asperities which are zones along the fault plane where frictional resistance virtually prevents movement. This causes large accumulation of strain energy and when the fault ruptures again a large amount of energy is released by movement along these zones.
Seismograms from the local network were all saturated. The record obtained at PHIVOLCS Central Office in Quezon City (QVP) (Figure 9) shows a part (three minute after the onset) where there is a high energy release but it is possible that this is already an aftershock. Nothing could be discerned from the first three minutes of the record which is contained the P-wave. However, if we obtain teleseismic records from distant stations like the one shown in Figure 10, it will be possible to infer asperities and this is the part of the P-wave with high amplitude pulses.
Using the Gutenberg-Richter travel-time chart (Figure 11) for normal focal depth earthquakes, one can expect two P phases, the Primary (P) wave (marked as P in the figure) and reflected P wave (marked as PP) to be recorded by a distant station approximately 3000 kms away. The seismogram shown in Figure 12 is a three-component, very broadband digital record obtained from Tottori Observatory in Japan, about 3000 kms. from epicenter. If the P-wave is expanded as shown in the figure, several strong pulses aside from the regular P phases earlier mentioned can be observed which may be inferred as due to asperities. Shibutani, et.al (1991) were able to distinguish these pulses and classified them as two sub event groups which occurred 20 secs and 50 secs from the onset. The first sub event ruptured the fault in the Nueva Ecija area while the latter sub event ruptured up to the northern terminus. It can also be observed that from the onset up to a few seconds, (marked as *), the rupturing process is slow and that the release of seismic energy is weaker.

 

FORESHOCK PATTERN
Figure 13 shows the background seismicity in the northern and central Luzon areas 1989. Most of the earthquakes are small and there seem to be no foreshocks in 1989 correlatable to the ground rupture trace.
During the six months (January to June 1990) preceding the main shock, there were plotted earthquakes which could be classified as foreshocks. These occurred on: 01, 06, and 13 April and 05 May. These were mostly small to moderate magnitude events (Ms between 3-5) and were plotted near the earthquake's epicenter, along and around the trace of the ground rupture (Figure 14). The 13 April 1990 (Ms 4.6) foreshock was felt at Intensity III (intensities are based on adapted Rossi-Forel Intensity scale of I-IX) at Pantabangan, Nueva Ecija, Manila and Baguio City.

 

THE AFTERSHOCK SEQUENCE
The first felt aftershock was reported by PHIVOLCS Baguio City field observer seconds after the main shock. This was closely followed by successive aftershocks we were recorded and felt every minute and by 23:55 GMT, 444 aftershocks were felt PHIVOLCS Baguio City station. At Baguio City, the first three aftershocks were felt at intensity VIII. The magnitudes of these varied from 4 to 6.
As expected of earthquakes with large magnitudes, the aftershock area covered a wide area. In Figure 15, the distribution of these aftershocks are shown. The plottings using the PHIVOLCS-Kyoto University digital seismic set-up is shown in Figure 16. The aftershock lie along the rupture trace and clusters around the Baguio area forming an east-west orients alignment.
In an E-W section (Figure 17) at 15.5 N. Lat., depths of hypocenters vary from 0 to 50 kms. In a NES section (Figure 18), the hypocenters are found also in the 0-50 kms range with some scatter of deeper earthquakes up to 200 kms.
Figure 19 illustrates overall aftershock pattern showing the abrupt decay in the number of aftershocks from July 1990 to December 1991. This pattern corresponds to type 1 of Mogi's (Mogi, 1963) foreshock-aftershock pattern (Figure 20) where there is no accelerating foreshock before a main shock, suggesting a homogeneous source rock and a uniform distribution of external stress.

 

FOCAL MECHANISM SOLUTIONS
The NEIC global network produced focal mechanism solutions for the main shock and F 12 aftershocks of the 16 July 1990 earthquake. In Figure 21, the sense of movement of the main shock is shown as left-lateral strike slip fault with very small vertical component. Table 4 shows the list of the earthquakes with focal mechanism solutions and are presented Figure 22. Along the ground rupture, the motion was left-lateral strike slip corresponding to observed displacements from the southern terminus near Gabaldon, Nueva Ecija to near Kayapa, Nueva Vizcaya. In Kayapa, solutions were thrust faults while eastward towards Baguio and Agoo, focal mechanism solutions suggests normal faulting. These events are also plotted in section as shown in Figure 23.
From the focal mechanism solutions, distribution of aftershock epicenters, interpreted landsat imagery of Baguio City (Figure 24, interpretations by R.S. Punongbayan) and field mapping of the trace of the ground rupture, we derived a hypothetical block model (Figure 25). This model shows that the dominant mechanism for strong aftershocks that occurred in the Baguio area is an extensional type of faulting which is in agreement with the sense of left-lateral movement of the main fault. This suggests the occurrence of thrust faulting in the Kayapa area and an E-W oriented normal faulting with minor right lateral strike slip component in Baguio. Such right lateral motion may be due to rotational motion due to the bending of the ground rupture line upon reaching Digdig Fault. The Baguio subfault failed to reach the surface which could explain the absence of ground rupture in the area. Likewise, the movement of the said subfault could have contributed, aside from topographic effect, differential site response and seismic wave radiation pattern, to the extensive damage in Baguio City.

 

CONCLUSIONS
       a. Aftershock distribution showed an east-west oriented alignment near the Baguio area with which a possible sub fault might be inferred.
      b. The inferred sub fault might have moved almost simultaneously with the rupturing of the main fault thru a series of sub events which propagated from the epicenter or might have moved as a big aftershock three minutes after the onset of the main shock. Aside from topographic effect, differential site response and seismic wave radiation pattern, the movement of this sub fault could have caused the strong ground shaking and heavy damage at Baguio and Agoo.
       c. The sense of movement of the sub fault as inferred from a focal mechanism of large aftershocks is a dip slip (normal) with small strike slip right lateral movement.
      d. The foreshock-aftershock pattern is a type 1 on the Mogi's (1963) classification and this suggests a uniform distribution of stress and a homogeneous source rock. This explains the reasons why there is no intense foreshock activity and for a less dense aftershocks distribution in the areas close to the epicenter (the point on the fault where rupturing initiated).

 

ACKNOWLEDGMENT
We would like to acknowledge the efforts of the technical and field personnel of PHIVOLCS with special mention to its Seismological Observations and Earthquake Prediction Division, Volcano Monitoring and Eruption Prediction Division and Instrumentation Section personnel. They provided very important earthquake data during and after the crisis for the consumption of the public and researchers. Some of these personnel braved the harsh and unsafe working conditions in the field and allowed themselves to be deployed in field assignments during the ensuing aftershock observations in Dagupan, Baguio and La Union areas. Likewise, our appreciation to those who stayed behind and processed voluminous earthquake data and disseminated information to a panicking public.

 

REFERENCES
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Neumann, F. 1966. Principles Underlying the Interpretation of Seismograms.
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Mogi, K. 1963. Some Discussions on the Aftershocks, Foreshocks, and Earthquake Swarms the Fracture of Semi-Infinite Body Caused by o7 3 an Inner Skess Origin and Its Relation to the Earthquake Phenomena (third paper). Bull. Earthquake Res. Inst., 41: 615- 658.
Morante, Edgar M. 1974. The Ragay Gulf Earthquake of March 17, 1973, Southern Luzon, Philippines. Journal of the Geological Society of the Philippines . 28(2).
National Power (Corporation. 1990. Seismic Event 16 July 1990 atAround 4:30 P.M.
Preliminary Determination of Epicenters Monthly Listing. National Earthquake Information Center. USGS. July to December 1990.
Punongbayan, R. S. and Umbal, J. V. 1990. Overview and Impacts of the July 16, 1990 It Earthquake. Proceedings to the GEOCON'90. V. 1.
Repetti, W.C. 1946. Catalogue of Philippine Earthquakes, 1589-1899. Bulletin of the Seismological Society of America. 36(3): 133-231.
Shibutani, T., T. Ohkura, Y. Iio, M. Kanao, K. Nishigami, K. Tasaki, T. Iwata,
Ekakehi, N. Hirano, M. Ando, B.C. Bautista J.P. Puertollano, A.G. Lanuza, A.A. Melosantos, A. V. Chu, R.P. Pigta in, Edwin De La Cruz, R. S. Punongbayan. 1991. Search for the Burried Subfault(s) of tho 16 July 1990 Luzon Earthquake, the Philippines Using Aftershock Observations. Journal of Natural Disaster Science. 13(1): 29-38.
Uy, E. A., B.P. Punsalan. 1985i Magnitude Calculations Using Time Duration. IISEE Participants Report.
Wennerberg, L., J. Bicknell, D.C. Garcia. Differential Ground Motions Near Damaged Structures in Baguio, Philippines, Recorded During August 1990. 1990 AGU Fall Meeting. Abstracts and Program.
Wennerberg, L., J. Bicknell, J. D.C. Garcia. 1990. Implications of Local Aftershock Recordings for Source Processes of the M 7.8 Earthquake of 16 July 1990. 1990 AGU Fall Meeting. Abstracts and Program.
Wennerberg, L., J. Bicknell, D.C. Garcia. 1990. Local Differences in Ground Motion Near Damaged Structures: Aftershock Recordings of the 16 July 1990 Philippine Earthquake. 1990 AGU Fall Meeting. Abstract and Program.
Wennerberg, L. 1991. Philippines Earthquake: Ground Motion and Soil Response. Abstract submitted for EERI annual meeting in Salt Lake City.

Salvador F. Reyes, Alexis A. Acacio, Frederick C. Parayno
and Narcisa P. Angelias
U.P., Engineering Research and Development Foundation, Inc.

PART I

INTRODUCTION

Liquefaction was widespread in various parts of Northern Luzon during the recent 16 July 1990 Philippine Earthquake which registered a magnitude of 7.8 on the Richter scale.

The Philippine government, through the Department of Environment and Natural Resources (DENR) and the Department of Science and Technology (DOST) is undertaking steps to mitigate the effects of future major earthquake not only in areas affected by the above mentioned event but also in other developed and liquefaction prone areas in the country. Part of that effort is the project study reported herein.

The focus of this study is to collect reliable geotechnical data on some areas which suffered major liquefaction damage during the 1990 earthquake and to generate from these a database which can be readily accessed and processed by a database management system or DBMS to provide information pertinent to the aforementioned DENR master project.

The present study covered liquefaction-damaged areas Dagupan City, Pangasinan; Agoo and Aringay in La Union, and the towns of Gerona and Pura in Tarlac. The widely used method of exploration by borings with standard penetration testing (SPT) was employed in conjunction with a procedure that is increasingly being used for liquefaction assessment - the Dutch Cone Penetration Test (CPT).

OBJECTIVES OF THE STUDY

This study was undertaken with the following objectives:

     1. To create an expandable database consisting of soil investigation results obtained by performing the Standard Penetration Test (SPT) and by the Cone Penetration Test (CPT);

1.         2. To set up computer software which can be used to access the database. Its possible use for assessing liquefaction potential in areas for which SPT/CPT data are available, is illustrated.

METHODOLOGY, FRAMEWORK

The study consisted of three main phases, namely:

          1. Field Investigation
          2. Laboratory Soil Testing
          3. Development of Database

 

1. Field Investigation
Reconnaissance Field Survey

A reconnaissance field survey was conducted prior to the actual field investigation. This was done to locate the specific borehole sites and map out the borehole location plan foreach area being considered.

Field Investigation

Field investigation by the SPT and the CPT was done at Dagupan City, and two towns each in La Union and Tarlac. The number of boreholes cone penetrometer test positions in each location are as follows:

	SPT	CPT
Dagupan City	5	21
Agoo, La Union	2	8
Aringay, La Union	2	11
Gerona, Tarmac	2	6
Pura, Tarlac	2	6

(Refer to Figures 1 to 5 for the borehole locations.)

 

Drilling Procedure

The SPT was done in accordance with ASTM specifications. For each test, a 2-inch (50.8 mm.) outside diameter split spoon sampler is driven a total distance of 18 inches (460 m.) by means of a 140 lb. (63.5 kg.) driving head falling free from a distance of 30 inches (760 mm.). The number of blows needed to drive the sampler in 6-inch ( 153 mm.) increments is recorded and the number of blows needed to drive the last 12 inches (300 mm.) is taken as the N-value. Soil samples were recovered using the spoon sampler and were taken to the soils laboratory for analysis and testing.

The CPT device consists of a conical point with a 60-degree apex angle and base area of 10 cm2 attached to a rod that loosely fits in an outer sleeve at the end of a hollow shaft. With the cone retracted, the assembly is pushed to position while the resisting force is measured. The shaft is then locked in position while the cone is pushed (about 5cm)at a slow steady rate. The measured resisting force is the cone resistance (Qc). The difference between this and the previously measured resistance to penetration of the assembly determines the friction ratio (F;R).

 

2. Laboratory Test Procedure

The laboratory tests performed on soil samples from the boreholes are briefly described as follows:

1. Classification of Soils for Engineering Purposes
The Unified Soil Classification System (USCS) was used to classify the soils.

2. Particle Size Analysis
Soil is passed through a series of sieves and the weight of soil retained in each sieve determined. A graph is drawn relating the percent finer by weight and the particle size on a semi-long scale. D50 or equivalent particle diameter (in mm) that equally splits the soil in coarser and finer fractions is read off from this graph.
3. Liquid Limit
The liquid limit is the moisture content at the point of change between the liquid and plastic states of the soil.
4. Plastic Limit
The plastic limit is the moisture content at the transition between the semi-solid state and the solid state.
5. Moisture Content
The moisture content is ratio of the unit weight of water to the weight of dry soil.
6. Specific Gravity
The ratio of the unit weight of soil in air to the unit weight of water 4ºC.

 

Development of the Database

A method of filing borehole data for the liquefaction phenomena is presented in this study. A set-of menu-driven application program, named "SOIL" was developed using Paradox Personal Programmer and Paradox 3.5, a relational data base management software(DBMS).

A script which causes the DBMS to translate data for input to the program for free field liquefaction analysis is described.

 

Description of " SOIL"

In the field investigation, SPT and CPT was conducted to obtain the necessary borehole data needed for the study. In the same manner, the storage of data is categorized into two, namely, the SPT data and the CPT data. All data gathered using the washboring (SPT) method are in the SPT Table while those data gathered using the Cone Penetrometer are in the CPT Table. Both data tables are stored in separate database files that are (conceptually) in tabular form and containing all field and (in case of the SPT) laboratory test data.

 

"SOIL" Menus The menu driven "SOIL" application program consists of four modules which are the following:

1. INQUIRY
2. DATA ENTRY
3. REPORT
4. FILE
Three of these modules (Inquiry, Data Entry and Report) contain the essential requirements of an information system. The FILE module on the other hand is a script that adapts data from the data tables (SPT and CPT tables) for use in the liquefaction program. The output of the program was the basis of the discussion presented in Part II of this report in evaluating potential liquefied areas.

The four modules are now described in detail.

 

INQUIRY

The main function of this module is enabling the user to view the stored borehole data in the data base files. The user is given the option of viewing either the SPT or the CPT table upon the selection of this menu. A selection is presented on the screen on the locality and the borehole number of the borehole data the user is interested in. For the borehole number selection, an approximate description of the exact location where the borehole was conducted is presented to the user for orientation. The movement of the cursor for the selection process is controlled by the arrow keys in the keyboard.

As an example, if the user wants to view the N-value of Bhno. 1 in Dagupan City 3 meters deep, he has to follow the steps as outlined below.

Steps:

1. Place cursor on INQUIRY and press return.
2. Place cursor on SPT and press return.
3. Place cursor on DAGUPAN and press return.
4. Place cursor on Bhno. 1 and press return.
When the steps are followed, all borehole data stored in the SPT table of bhno. 1 in Dagupan City can be viewed on the screen. All data stored for the specified borehole can not be viewed all at once due to limited screen space. Viewing data not displayed on the screen can be done with the use of the arrow keys. Horizontal and vertical movements is controlled by the arrow keys. Viewing of data can be in Tabular form or in Form View by toggling F7.

 

DATA ENTRY

The functions of the module can be categorized into two. The first function is mainly the addition of new borehole data in either the SPT or the CPT table. The other function is editing previously stored data either by correction of data information or by deletion of stored data in both the SPT and CPT tables.

When this menu is selected, two selection is presented to the user namely ADD and EDIT with the functions mentioned above. When either is selected, the user is then presented what table he intends to work into (SPT or CPT). As in all DBMS, cursor movement is controlled by the arrow keys.

For example, when the user wants to enter new borehole data in the CPT table, he has to place the cursor on the following heading and press return.

Steps:

1.Place cursor on DATA ENTRY and press return.
2. Place cursor on ADD and press return.
3. Place cursor on CPT and press return.
In the same manner as in viewing data, addition or editing of borehole data can be done in Table view or Form view by toggling F7.
Tables 1 and 2 contain the list of data information as organized in the SPT and CPT tables respectively.

The location is the locality where the borings were undertaken. As an example, for a boring done in Dagupan City, Pangasinan, DAGUPAN is entered in the location field name.

A method of identifying approximately the specific location of the boreholes is to know the global orientation in terms of the Latitude (due North) and Latitude (due East). These are borehole indentifiers but when data can not be obtained on the Latitude and Longitude of the the borehole, this can be left blanked. When data is available though, the input format should be as follows.

XX° - XX' - XX"

For example, SPT borehole no. 1 in Dagupan City, Pangasinan has a latitude of 16º2' 36.7" and a longitude of 120º 20' 23.6". In the SPT table the latitude is entered as:

16 - 02 - 36.7

and the longitude as:

120 - 20 - 23.6

 

REPORT

The main function of this menu is the production of the stored data in paper form with the use of a printer. Entering the locality and the borehole number is a requisite in this menu before printing of the needed data. It is assumed that the user has viewed the table and therefore is already familiar with the location and borehole number he is about to print. For example, to print CPT borehole no. 3 in Aringay, La Union, the user has to place the cursor in the following heading: REPORT, and CPT and press return key for each selection. Then the user is asked the location, wherein he is to type ARINGAY (in capital letters). After pressing the return key the user is asked the borehole no. wherein he is to type 3 in the keyboard. After this, printing of CPT borehole no. 3 in Aringay, La Union commences. The printed report contains all the stored information for the specific borehole as organized in the tables.

 

FILE

The main function of this module is to gather the data needed for the liquefaction program and convert these data into text file which is a requisite of the liquefaction software program. This module illustrates how data stored in this manner can be accessed for a specific user's purpose. Using the converted text file from the table and the liquefaction program, analysis of the liquefaction damaged areas is presented in Part II of the report. Data gathering and conversion can be done per locality in this module. As an example, to use SPT borehole data

in Gerona, Tarlac for the liquefaction program, the user places the cursor under the following headings: F1LE, SPT and GERONA respectively for conversion to text file. The data are then automatically stored in QUAKE.TXT. To access these data use any text editor and use the file name mentioned above where they were stored. When the FILE module is used again, the data text file supersedes the data text file previously stored.

 

NOTE: The field type is classified into two namely: A (Alphanumeric) and N (Numeric). Alphanumeric type are followed by the number of characters the field type can accommodate. If there is an excess of characters entered into these held it can only access the characters stipulated above (refer to Tables 1 and 2). As an example, A7field type can only accommodate seven (7) alphanumeric characters. The numeric field type on the other hand can only accept numbers in its field The numbers will be stored as is but screen display is limited to two decimal places. (Refer to LEGENDS for the definition of the field name in Tables 1 and 2).

 

CONCLUSIONS AND RECOMMENDATIONS

The Standard Penetration Test (SPT) and the Cone Penetrometer Test (CPT) are two of the common methods of gathering soil data for geotechnical purposes. Availability and familiarity with the equipment utilized facilitated the data gathering process of the study. Valuable information were obtained from the said tests even though these tests were performed after the earthquake, when soil conditions may have changed relative to the pre-earthquake state. The gathered borehole data from the affected areas can be the preliminary step in conducting further study in correlating the liquefaction phenomena to available borehole data on potential areas.

A database has been created to store information gathered from the areas damaged by liquefaction during the July 1990 earthquake. This information can be conveniently utilized and processed to provide technical information to researchers as well as practitioners. Furthermore, this database is also designed to receive additional information not only on the areas covered by this study but also for immediate expansion to cover other areas as data from these areas become available. The long term value of this database is in its capability to continuously receive and process additional soil boring data. As the number of available data is increased, a more accurate analysis of the liquefaction phenomena based on the field data from the areas that actively liquefied as well as those that did not become possible

The use of the CPT is especially advantageous. It can be done relatively quickly, avoids problems of soil disturbance, and provides a nearly continuous record of relevant soil parameters to a depth of 10 meters or more provided the soil is not too dense. In any effort to map liquefaction prone areas in the country, it is recommended that the CPT be primarily employed. Minimal borings would still be needed, however, to determine index properties. Additional work of this nature would also help firm up correlations between CPT and SPT values necessitated by the fact that assessment of liquefaction potential is currently still based primarily on the latter.

Although the Cone Penetrometer Test provides no samples for laboratory analysis specifically, textures at different depths - these can be deduced from the Friction Ratios (FR) based on correlations established by Schmertmann and others. A graph of the Friction Ratio (FR) with respect to depth in all the CPT boreholes in the liquefaction-damaged areas is presented in Fig. 6. Generally, the graphs indicate a predominance of cohesionless (siltsand) materials in the surveyed areas.

The cone resistance (Qc) is a significant information that can be gathered in employing the CPT, primarily because it is a measure of strength or bearing capacity of the soil. Graphs representing the cone resistance (Qc) of the areas surveyed with respect to depth ill each borehole is shown in Fig. 7. Generally, the graphs indicate an approximate value of less, than 10 MPa for depths not greater than 10 meters in the damaged areas, except in La UDi0n w where there are values way above the approximate value for certain depths. 5

The D50 (diameter at 50 % passing, in mm) can be inferred from the grain size analysis of the laboratory testing in the SPT. This basically exhibits the grain size of the soil at sampling depths. Graphs of the D50 with respect to depth for the locations in the study 10 t presented in Fig. 8. The graphs confirm that silty to fine sandy materials generally composed the liquefaction damaged areas.

A correlation of the N-value (of the SPT) to the cone resistance (of the CPT) is graphically exhibited in Fig. 9. illustrating the usefulness of maintaining a database in this form for liquefaction-related studies. The graphs indicate a lower value for the cone resistance | gathered in the study as compared to the value (in dotted lines) recommended by Seed and Idriss (1982).

 

NOTE: For liquefaction program, the data needed are the depth, N-value and D50. Obviously these data (N-value arid D50) can only be obtained with the SPT method. For our purpose, the cone resistance (Qc) of the CPT method was correlated with the N- value of the SPT using suggested correlations by Seed and Idriss (1982). The D50 on the other hand that was entered in the CPT table were adaptations from the SPT borehole performed within the vicinity of the CPT boreholes which will approximately yield the same value.

 

 

PART II

INTRODUCTION

Part I of this report describes the processes of generating and managing SPT and CPT field data using Paradox 3.5. In Part II, a method of accessing the database file is presented and used for specific purpose - the assessment of liquefaction potential of the areas surveyed. The database file can be similarly accessed by engineers researchers and planners for their purposes and needs.

 

LIQUEFACTION PHENOMENA

Soil liquefaction is experienced if a saturated sand deposit is subjected to ground movements (earthquakes) which tends to densify (decrease in volume) the deposit, thereby, increasing pore water pressure if drainage is inhibited. The build up of pore water pressure will reach a point wherein it becomes equal to the overburden pressure rendering the effective stress ineffective or equal to zero, thereby developing a liquefied state. Liquefaction in the upper layer of a deposit may also occur due to the liquefaction in the underlying layers of the deposit. This is due to the upward propagation of the excess hydrostatic pressure in the liquefied zone which will induce a liquefied condition in the upper surface layers.

A clear manifestation that liquefaction occurred in the deposit is the formation of sand boils and mud spouts at the ground surface or the development of quick-sand like conditions. In the areas covered by the study, these conditions were observed especially in Dagupan City where excessive tilting of buildings and the floating to the ground surface of underground tanks of gasoline stations were experienced.

The most common procedures in assessing liquefaction potential of soil deposits are presented by the American Association of State Highway and Transportation Officials (AASHTO) and the Japanese Society of Civil Engineers (JSCE). Based on the JSCE 1971 specifications, the soil deposit is likely to liquefy if the following conditions are met,

1. depth at 10.0 meters from the actual ground surface
2. N-value is less that 10
3. coefficient of uniformity is less than 6
4. D20 = 0.04 ~ 0.5 mm.
But these criteria were later revised to incorporate other data gathered in earthquakes where liquefaction was clearly observed. The 1980 JSCE specifications that the following conditions are conducive to liquefaction:

1. Sandy layers within 20.0 meters from ground water table and within 10.0 meters from the ground surface
2. D50 = 0.02 ~ 2.0 mm.
The AASHTO method suggested two approaches in evaluating liquefaction potential of a saturated sand deposit subjected to ground shaking which are:

1. Empirical methods based on field observations of the performance of sand deposits in previous earthquakes, correlations between sites which have and have not liquefied, and Relative Density or Standard Penetration Test blow counts (N-values).
2. Analytical methods based on the laboratory determination of the liquefaction strength characteristics of undisturbed samples and the use of dynamic site response analysis to determine the magnitude of earthquake induced shearing stresses.
In both procedures, the AASHTO method requires the ground acceleration at the site as a prerequisite for assessing liquefaction potential.
For the present study, both the ISCE and the AASHTO methods were utilized in assessing the liquefaction potential of the soils in the areas or localities covered by this study. Software based on the two approaches was used. In the absence of firm data, it was assumed that the peak ground acceleration at all sites was 0.25 g.

 

ANALYSIS

1. ARINGAY

The AASHTO Table indicated that the borehole located near the National highway (Aringay 2) gave a factor of safety (against liquefaction potential) for the upper 3.0 meters, way below the accepted value. The factor of safety ranging from a high of 0.63 for a depth of 3.0 meters and a low of 0.55 for a depth of 2.0 meters is basically composed of particles ranging from 0.02 mm. to 0.05 mm. as can be seen from the D50 column in the table. The relatively low values for the factor of safety can be attributed to the field N-values ranging from a low of 4.0 to a high of 7.0.

The 7.5 meter to 9.00 meter depths for the same borehole also yielded a factor of safety less than one but not as low as for the upper 3 meters. The factors of safety have a value of 0.94 for the 7.5 meters depth and 0.99 for the 9.0 meter depth. The D50 for the said depths are generally fine sand particles and ranges from 0.48 to 0.5 mm. The low factor of safety for these depths is more or less confirmed by the JSCE method which gave a value of 1.08 for the 7.5 meters depth and 1.14 for the 9.0 meter depth. But for the upper 3.0 meters the ISCE gave a relatively high factor of safety which may be due to the D50 particle for the upper 3.0 meters which is silt and may have a lesser possibility of liquefying as compared to sand. The hard strata for the borehole or refusal for the Standard Penetration Test was at a depth of 12.0 meters. This characteristic of the borehole soil data in relation to refusal is firmly established by the other borehole (Aringay 1) located near the sea (Lingayen Gulf), approximately 3.0 km. from the location of Aringay 2. The table on the liquefaction potential of Aringay 1 is basically the same with Aringay 2 with the following notable differences. For Aringay 1, the upper 2 meters below ground surface is below the accepted value for the factor of safety, as against 3.0 meters for Aringay 2, and the soil composition with a 50% passing (D50) is more of fine sand particles. The 7.5 and 9.0 meter depth characteristic are basically the same as in Aringay 2. It can be said that the area surrounding the boreholes (Aringay 1 and Aringay 2) where the data was gathered, is hard strata 12 meters below ground surface and has a tendency to liquefy on the lower 2 to 3 meters below the ground surface and a lesser possibility to liquefy on the 7.5 to 9.0 meters below ground surface.

2. AGOO

The table identifying the liquefaction potential of the borehole indicates that Agoo 1, an SPT borehole located more or less on the sandy beach of San Isidro, Agoo, La Union, has a 50% passing composed mainly of fine sand particles at a depth of 1 meter below the ground surface indicating the greater possibility of liquefying as shown in the AASHTO table but is relatively safe with regards to the JSCE method. Refusal is attained at a depth of 10.5 meters below ground surface which is more or less the same with Agoo 2, located also on the beach of San Isidro, Agoo, La Union, roughly 2 km. away from Agoo 1 where refusal was attained at a depth of 12.0 meters below ground surface. As can be observed from the boreholes of La Union (Agoo and Aringay), the data indicate that 12.0 meters below ground surface is hard strata. But unlike in Agoo 1, Agoo 2 indicates that six meters below ground surface has potentials of liquefying, specially the 2.0 to 6.0 meter range below ground surface using the AASHTO table. But using the ISCE table gives us a factor of safety within the limit but relatively low in depths (2.0 to 6.0 meters) ranging from 1.17 to 1.19 as compared to other depths. The water table for both boreholes are above 1.0 meter below the ground surface. It can be noted that the factor of safety increases as there is an increase in depth for both boreholes. The possibility of liquefaction is confined to the upper 1.0 meter of the soil area.

3. GERONA

From the AASHTO table, a borehole within the town's main plaza (Gerona 1) indicates that liquefaction must have occurred on the upper 2.0 meters from the ground surface and the lower 9.0 to 11.5 meters from the ground surface. But from the D50 data, as can be seen from the table, it is more likely that the liquefaction is on the 2.0 meter upper layer because it is composed of fine sand particles with very low field N-values. The other depth, which is the 9.0 to 11.5 meters, may also have low field N-values but their soil composition from D50 is mostly silt and clay which has a lower possibility of liquefying and the N-values for these depths, assuming clay and silt is the dominant soil condition, indicates that the strata is stiff. This may also account to the high factor of safety against liquefaction as produced in the ISCE table. Gerona 2, a borehole located on the town's residential areas very near the plaza is quite different from Gerona 1. The soil profile as seen from the AASHTO table reveals many possibilities for liquefaction, which are the following:

1. up to 2.0 meters from ground surface
2. 5.0 to 7.0 meters below ground surface
3. 10.0 to 14.5 meters below ground surface
4. 19.0 to 20.0 meters below ground surface
In consonance with the ISCE table in assessing liquefaction potential for this borehole, only the 5.0 to 7.0 meters below ground surface has the high tendency to liquefy. The explanation for these is that from the D50 column, the 10.0 to 14.5 meter range below 4c ground surface and the 19.0 to 20.0 meter range below ground surface is basically composed of silt to clay particles which has a lower possibility of liquefaction, explaining the high factor of safety in the JSCE table. Gerona 1 has a water table depth of 1.35 meters while that for Gerona 2 is 0.35 meter below the ground surface. The refusal for the boreholes was not achieved at the designated limit of boring depth which is 20.0 meters. Gerona 1's born stopped at 11.50 meters due to a log which was hit by the drilling team, making it impossible to continue on with the probe for this borehole at a lower depth, but at the same time indicating that the field N-values preceding this depth is quite low. However, in clay soil conditions, this may be stiff in terms of soil classification.

4. PURA

A notable observation for both boreholes in Pura, Tarlac (Pura 1 and Pura 2) is the 50% passing which is generally silt and clay particles from 5.0 to 20.0 meters below the ground surface and the first 5.0 meters below the ground surface made up mostly of silt to fine sand particles. It can also be observed that, using the JSCE table with the borehole data gives us a relatively high value for the factor of safety against liquefaction which can be attributed to the clayey soil particles from the D50 column, indicating a lower possibility for liquefaction as presented by the JSCE method which limits liquefaction to sand particles of these with D50 not less than 0.02 mm. Based on the AASHTO table, for Pura 1 which is located in the arca of the municipal building, the depth of up to 13.0 meters below the ground surface has high potential for liquefaction. For Pura 2 which is located within the public school roughly 1.5 km. from the location of Pura 1, the liquefaction potential extends up to 20.0 meters below ground surface mainly due to the low factor of safety as indicated in the AASHTO table. The field N-values for both boreholes are relatively low, but the JSCE table gave a high factor of safety for both boreholes having 1.4 as the lowest value which may be due to the clayey condition of the soil making it relatively stiff even with low field N-values. The water table depth of Pura 1 is 0.95 meter below ground surface and Pura 2 is 1.5 meters below ground surface which is quite normal.

5. DAGUPAN CITY

Some of the observations noticeable from the gathered field data of Dagupan City are the following:

1. refusal was not attained in any borehole down to the depth limit of 20.0 meters.
2. generally, the first 15.0 meters below the ground surface has a 50% passing (D50) compose of silt to fine sand particles and the lower 16.0 to 20.0 meters from the ground surface has a 50% passing (D50) composed of silt clayey particles.
3. the field N-values are relatively low.
The detailed observation of each borehole are the following:

Dagupan 1, a borehole situated near the vicinity of the collapsed Magsaysay bridge, indicates that the first 7.0 meters below the ground surface with fine sand particles has a high liquefaction potential, thereby giving low factor of safety values from the AASHTO table s and the JSCE table with the former giving a more conservative value. Another liquefaction potential exists below 16.0 to 20.0 meters below the ground surface based on the AASHTO table but not confirmed by the JSCE table, due to the clayey soil conditions in these range of depths. But for both depth consideration, the field N-values are very low compared to the N-values of different depth in this borehole.

Dagupan 2, a borehole situated on Nable Street across the Pantal River at the back of A.B. Fernandez Avenue, indicates that the first 2.0 meters below ground surface and the range from 9.0 to 20.0 meters below the ground surface are potential liquefaction zones. This is validated by the low field N-values gathered for both zones. But the upper layer is more prone to liquefaction due to its sandy characteristics unlike the lower zone that is clayey in nature, which is confirmed by the JSCE method.

Dagupan 3, situated at the back of the damaged buildings of A.B. Fernandez Avenue, indicates that the entire 20.0 meter depth below ground surface has a high liquefaction potential based on the AASHTO table and on the field N-values. The factor of safety against liquefaction for this borehole ranges from 0.11 to 1.57 meter with an average of 0.623, the lowest among the borehole data gathered for this research project. The average is for the full 20 meters deep borehole. But the JSCE table gave only the first 4.0 meters below the ground surface as a potential liquefiable zone due to its fine sand characteristics, which makes the field N-values very loose in classification.

For Dagupan 4, located between A.B. Fernandez Avenue and Perez boulevard and within the vicinity of the McAdore Hotel, using the JSCE table indicates that the borehole has low potential for liquefaction giving high values for the factor of safety but using the AASHTO table, the following are potential liquefiable zones:

1. 3.0 meters below ground surface
2. 8.0 meters below ground surface
3. 13.0 to 14.5 meters below ground surface
The following liquefiable zones as identified in the AASHTO table gave low field N-values ranging from 3.0 to 12.0 meters. But the 13.0 to 145 meter range below ground surface has a 50% passing (D50) composed of silty to clayey particles making it less likely to liquefy than the other two zones.

Dagupan 5, located along Malued Road, is basically like Dagupan 4 wherein wk1 JSCE table is used, the area is not potentially liquefiable but with isolated layers liquefiable 1 using the AASHTO method, which is confirmed by the low field N-values in the following depth range:

1. 1.0 meter below ground surface
2. 8.0 meters below ground surface
3. 11.5 meters below ground surface
4. 19.0 to 20.0 meters below ground surface
The water table depth for the borehole is 1.5 meters below ground surface thereby making (1) unlikely to liquefy. Horizons (3) and (4) have clayey particles from D50, reducing their susceptibility to liquefaction, leaving the 8.0 m horizon the only one likely to liquefy.

 

CONCLUSIONS AND RECOMMENDATIONS

Generally, soil condition of areas affected by liquefaction will not be altered as a result l of the earthquake. Following this assumption, therefore, the factor of safety tabulated for each location using both the JSCE and the AASHTO methods may reasonably represent the soil condition both before and after the earthquake. Hence, in the analysis of each borehole in the areas affected, the layers designated to be potential liquefiable zones may have actually liquefied during the July 16, 1990 Philippine earthquake.

Taking the value of 1.5 from the tabulated results for the factor of safety against liquefaction potential as the margin in designating potential liquefiable or non-liquefiable layers, the following soil conditions are the outcome for the potential liquefiable layer

1. loose soil classification
2. upper layers of the surveyed areas
3. water table near the ground surface
4. N-value of less than 30 using the AASHTO method and less than 35 using the JSCE method
5. 50% passing (D50) of approximately 0.001 ~ 1.8 mm.
A liquefaction evaluation procedure is recommended for the construction of future structures in the areas surveyed and other areas suspected to be potential liquefaction areas. This evaluation procedure can be realized with the following suggested steps:

1. Analyze the area being considered using the data presented in the report.
2. If necessary, conduct soil boring test or gather available data on areas not covered by the research.
3. Compute the factor of safety based on the borehole data by using AASHTO the of the JSCE methods in assessing liquefaction potential as presented in Part II of the report.
4. Using results of 3 and the available borehole data design the foundation of the structure with the appropriate scheme.
Pile foundations are effective in minimizing if not eliminating damage to structures, as evidenced by the apparently undamaged structure of Macador Hotel in Dagupan City. Use of piles, unfortunately, is uneconomical for low or medium-rise structures. Well-tied footing foundations may, in these cases, provide a measure of protection by way of minimizing differential settlement and spreading (hence, structural damage) when subsoils liquefy. Supporting evidence in this regard may also be discerned from the behavior during the earthquake of some buildings in Dagupan City.

 

REFERENCES

Earthquake Engineering Committees, Japan Society of Civil Engineering. 198?, Earthquake Resistant Design.

Lambe, T.W. & R.V. Whitman. 1969, Soil Mechanics. N.Y.: John Wiley.

Seed, H.B. & I.M. Idriss. 1982, Ground Motion and Soil Liquefaction During Earthquakes. Earthquake Engineering Research Institute.

David C. Hopkins, BE(Hons).PhD Ceng, FIPENZ MICE
Director KRTA Limited, Wellington New Zealand
Currently Program Technical Specialist, Earthquake Reconstruction Project DPWH, Manila

INTRODUCTION

The earthquake of July 16, 1990 was notable for its widespread effects and range of types of damage. As such it provides a unique opportunity for engineers to review their approaches to seismic resistant design.

This paper results from the author's involvement in a technical reconnaissance visit immediately after the earthquake, and his subsequent role in the Philippine Government's Earthquake Reconstruction Project. Damage, and lack of damage, has been viewed first hand. Reconstruction, and strengthening measures have been reviewed and observed on a range of projects. Contact with local consultants and government engineers has provided further insights into the effects of the earthquake and the key issues faced in the design and construction of seismic resistant buildings and infrastructure.

There is much to be gained by sharing and discussing the effects of the July 16 Earthquake, and it is hoped that the following observations will assist in providing buildings and infrastructure of increasingly better seismic performance.

The July 16 Earthquake and its Effects.

The range of types of damage and its widespread geographic location is indicated by the following.

• Baguio suffered major losses to buildings, especially hotels.

Dagupan lost a key bridge and many buildings subsided due to liquefaction of foundation soils.

Major roads in the mountain regions were devastated by landslip which exposed slopes to subsequent rains.

• Roads on the plains were extensively damaged by liquefaction.
  Many bridges on national, provincial and barangay roads were damaged due to landslip and liquefaction.
  Hundreds of schools and hospitals over a wide area were damaged or destroyed due to ground shaking,liquefaction and ground subsidence.
  Several areas suffered damage directly attributable to fault movement, particularly to roads.
  Damage to natural environment was substantial. Slope failures laid bare soils which eroded in subsequent rains. Siltation closed hydro dams and has modified river beds, making flooding in subsequent rains much worse in some areas.

Several technical publications have recorded the effects of the earthquake in some and indicated likely key issues. These are covered in detail in References 1, 2, 3, and 6. The Summary from Reference 1 is reproduced as Appendix A for ease of reference.

 

Earthquake Reconstruction Project

The Earthquake Reconstruction Project (ERP) was initiated by the Government of Philippines under Republic Act 6960 and provides for the reinstatement, and/or strengthening of damaged public facilities. The ERP is funded by the Philippine Government with the backing of loans from the Asian Development Bank (US$ 100 million) and World Bank (US$ 125 million).

There are over 12,000 sub-projects in the Earthquake Reconstruction Project which includes all work from plastering cracks to replacement of major buildings and bridges. Quite apart from the technical challenges, this represents a considerable organizational task. Many of the major consultants in Manila are playing key roles in managing this effort by carrying out designs and supervising construction. This is being done through an overall management structure headed by Department of Public Works and Highways (DPWH) Central Office and implemented through DPWH Regional Offices. Each Consultant has been assigned a geographic area and is responsible for all projects implemented by DPWH in that area.

Other agencies such as the Department of Health (DOH) and the National Irrigation Administration (NIA) are responsible for implementing projects involving their facilities.

Figure 1 shows the basic organization of the earthquake reconstruction project.

Important Features of the ERP are:

1. Reconstruction and Repair of

• Highways
• Bridges
• Roads
• Housing
• Hospitals
• Schools
• Flood Control Works
• Water Supply
• Irrigation Systems

2. The establishment of a Project Implementation Unit and a Project Coordination Unit within DPWH to:

1. Oversee implementation.
2. Incorporate mitigation and preventive measures to defined standards.
3. Make application to ADB and WB for loan funds.
4. Coordinate the efforts of the various agencies.

International Consultants assigned to the ERP include Implementation Specialists Technical Specialists.

3. The focus of Technical Specialists is on incorporation of mitigation measures ink reconstruction.

Particular tasks of Technical Specialists include.

1. Preparation of Detailed Guidelines for Design & Construction
2. Establishment of mitigation measures
3. Review of design criteria and preparation of contract documents
4. Review of site investigations
5. Review of engineering supervision
6. Provision of training in mitigation technology and its application in construction

4. This requires

1. Liaison with DPWH and other implementation units
2. Liaison with Local Consultants responsible for design and supervision

Projects must meet ERP criteria to qualify for funding from the loan agencies. This is particularly relevant to the incorporation of satisfactory mitigation measures.

Table 1 is a summary of Physical Accomplishment in the project as of December 31, 1991 and provides an insight into the range and number of projects in each category, as well as progress to date.

The majority of projects are of relatively low value and the efforts of the Technical Specialists are focused on projects involving significant reconstruction/ strengthening and technical content.

 

Main Lessons from the July 16 Earthquake

These may be summarized as follows:

1. Sound structural concepts must be adopted.
2. Careful detailing of structural elements and connections is essential.
3. So-called "Non-Structural" elements must be taken seriously
4. The importance of good construction practices and effective supervision must be recognized.
5. Special care must be taken in site selection, design and construction of bridges
6. Full account must be taken of soil conditions before design and during construction
7. Data gathering on seismic risk needs to be augmented. This is not a long list, nor are the issues new or particularly unique to the Philippines. But let us examine each in more detail to highlight some of the particular aspects which apply to the Philippines.

A. Sound Structural Concepts

Many of the hotels which collapsed in Baguio had soft storeys. That is, the lower one or two storeys had fewer partition walls than the upper floors. Earthquake energy is cow centrated in these flexible parts and places very high demands on columns and walls. Such demands would test the best columns, and soft storeys are universally recognized as dangerous. Examples from Baguio include the Nevada, FRB (Figure 2) and Royal Hotel where dramatic collapses occurred. If the architects and engineers for these hotels had got together early in the designs the soft storeys could have been eliminated without detriment to the architectural objectives.

Irregularities can be more subtle as was the case in the Skyworld building in Baguio. This triangular shaped building occupied a prime corner site on Session Road and had reasonably regular stiffness except for two floors at the lower end. This produced a partial soft storey which caused irreparable damage to the lower columns, resulting in the building being condemned. While it is true that better detailing of the columns may have saved them, the fundamental problem was the change in stiffness at the lower levels.

Another dramatic example of a soft storey was the collapse of the Library at the Central Luzon State University (Figure 3). This building had numerous walls on the first floor and a stiff wall facade on the 3^rd floor. By comparison the 2^nd floor, which housed the reading rooms, was without walls except around the central stairways. The collapse of the 2^nd floor was almost certainly a direct result of this soft storey effect. A more uniformly stiff structure such as shear walls for this building would have saved it.

A more subtle conceptual deficiency probably contributed to the collapse of the tower block of the Hyatt Regency Hotel in Baguio. In plan it had shear walls of seemingly adequate size in both directions, as shown in Figure 4. But verbal reports of the building motion in previous earthquakes suggested a marked torsional response. It is clear from the plan that the torsional stiffness is very much less than the transverse stiffness and it is possible that the inter-storey drifts due to torsional motion helped cause one of the outer columns or walls to collapse. Some stiffer elements restraining torsional movement may have prevented this.

It was evident from inspection of the collapsed building that detailing of the reinforce the columns and walls was deficient in modern day terms, but even so, provision to restrain torsion in the conceptual design may have saved the day.

So much for the failures which underline the importance of sound structural concepts. Many buildings did not fail.

In Baguio City, most of the buildings of up to five storeys made of reinforced concrete frames with block infill, survived the earthquake. Although the block was no doubt classed as "non-structural" by the engineers, it acted like a shear wall. Fortunately, in those buildings which survived, these walls happened to be reasonably symmetrically placed and continuous through the height of the buildings. It appears that in buildings of limited height the r forces in these shear walls did not exceed their strength. It would be helpful to learn more about the reasons for their survival.

As a final example, let us examine briefly some school buildings strengthened under the Earthquake Reconstruction Project. These projects illustrate a welcome understanding of the need for regularity in placement of shear walls and a recognition of the limitations of block-work to take earthquake loads.

The concept adopted for these two and three storey schools was to replace selected CHB walls with reinforced concrete (See Figure 5). Thus, reliable elements protect the columns and CHB walls from interstorey drift. The practical difficulties of placing these new wall elements are considerable, but because the concept is sound, the achievement of high quality becomes less critical, and good earthquake performance can be expected provided construction is satisfactory.

In summary, it is clear that:

A sound structural concept may offset shortcomings in detailing, but even the most careful detailing will not make up for shortcomings in the concept.

The lesson is: Make sure you are happy with the concept before starting on analysis and detailing.
 

B. Detailing of Structural Elements

It is well known that for reinforced concrete to behave in a ductile manner, it must be properly detailed (Figure 6). Most importantly this means:

1. Close-spaced stirrups and ties in columns and walls to hold the concrete in place and to prevent the buckling of longitudinal bars.
2. Close-spaced stirrups and ties in potential plastic hinge regions of beams to ensure they retain strength during cyclic loading.
3. Detailing of special transverse steel through beam-column joints in ductile frames maintain the integrity of the joint during plastic deformation of adjacent beam hinges
4. Careful attention to connections between all elements on the paths of gravity and earthquake load.

Points (a) (b) and (c) have for some time been covered by the Structural Code of Philippines in the Special Appendix for seismic requirements. Point (d) is fundamental to all structural engineering.

The author has reviewed many sets of drawings for schools, hospitals and other public buildings in the Earthquake Reconstruction Project. Very few have included provisions for points (a) (b) and (c) in spite of these being code requirements. Attention to point (d) has not been consistent.

Concrete Confinement

Laboratory tests on reinforced concrete which is properly confined by stirrups/ties have consistently shown the beneficial effects and are the basis of code requirements in earthquake prone countries. Extensive tests have been done on both column and beam sections.

Reference to Figure 7 gives a graphic illustration of this effect - strength is increased and ductility greatly enhanced.

Beam - Column Joints

Early tests on beam-column joints quickly revealed poor performance of the joint region. This led to a closer analysis of the forces on the joint region. Special vertical and horizontal steel is needed though the joint region to take the shear forces imposed by the beam hinge forces during cyclic loading.

The July 16 earthquake provided many examples of failures due to widely spaced ties and inadequate detailing of the main supporting elements of the structure. Frequently, the emphasis in the drawings (and therefore the design) was placed on detailing slab reinforcement and beam reinforcement-at typical sections. Attention to the beam/column joints and the columns themselves was markedly less. This emphasis should be reversed. The columns hold up the floors and the joints maintain the integrity of the building frame. On the other hand floor slabs and typical beam sections normally have considerable reserve of strength and an ability to redistribute load. Details of column reinforcing should be shown for the full height from foundation to the roof, i.e. a full elevation. Special large details of joint steel should be drawn for every separate case. The designer must build the reinforcing cage in every detail in his/her mind and then see that it is drawn in a clear and unambiguous way.

Base Fixity of Columns

When locating sections of columns requiring close-spaced ties, designers must consider the real situation, not an imaginary one. One frequent omission is the section of columnar immediately above the ground slab. Stirrups are close spaced immediately above the foundation (Figure 8) but not above the ground slab. It is argued that the floor slab is separated from the column so that the maximum moment occurs at the foundation. This assumption has two major drawbacks:

1. Murphy's Law says that the intended gap will not achieve its purpose, and therefore the column at ground floor level will be loaded.
2. By assuming fixity at foundation level, greater moments are induced in the column requiring more steel. It would be more economical and structurally sound to make use of the available couple generated by the floor slab and the footing base (Figure 8).

In addition, there is an inherent drawback in separating the ground floor slabs from the columns and walls. The opportunity is lost to hold these important elements together at ground level. This vital seismic improvement is available at little or no cost. The slab and reinforcement are in place and only a few starters are needed.

In summary: 

Columns and joints should receive more attention for both designers and their draughtspeople.

C. "Non-Structural" Elements

There are two major aspects to this:

1. The ability of "non-structural" elements, notably concrete hollow block (CHB) walls to alter the assumed structural response.
2. The tendency for "non-structural" elements to be damaged as the building sways.

The first aspect results in a real danger of building collapse. The second results in more costly damage, even in moderate earthquakes, and may even result in the unnecessary abandonment of the building.

The general failure of the engineering and architectural professions in the Philippines to address the structural implications of "non-structural" elements represents a major impediment to the improvement of the seismic performance buildings in this country. This failure resulted in unnecessary damage in the July 16 earthquake, and it is important that widespread and concerted efforts be made to learn from this experience and adopt a more reasons approach.

The situation can be addressed at relatively low cost, but requires a change in approach. Fortunately, there is evidence in some quarters that this change is happening.

Let us look at some examples

In almost all the public buildings reviewed by the author, including schools, hospitals, municipal buildings and universities, a reinforced concrete frame structure is used. Partition walls are built of CHB and tied directly to and not separated from the reinforced concrete frame.

And yet, invariably the designers state that they have designed a ductile moment resisting frame and the CHB is "non-structural ". Unfortunately the July 16 earthquake showed up the serious consequences of this engineering "blind-spot". Thus the placement of "shear walls", (i.e. CHB) was left to the whim of the owners or architect.

Many of the collapsed hotels in Baguio had soft storeys because of the participation of "non-structural" walls in the structural response.

In the Science Building at the University of Baguio (Appendix A, page 8) and at Montepino Apartments, a section of CHB wall fell out resulting in irreparable damage to columns. It is hard to escape the conclusion that had these wall elements been considered as having a structural role, the buildings would not have been structurally damaged to any significant degree.

On the second aspect of premature damage, there are countless examples of CHB walls which cracked in the July 16 earthquake. These were walls classified as "non-structural" by the designers. Unfortunately a stiff element attracts earthquake load, at least until it cracks. Thus, until it the blockwork is wrecked, the reinforced concrete frame takes little or no load. There are two points worth making about this premature damage:

1. It is frequently regarded as structural damage by the occupants and owners, and on occasion this resulted in evacuation of the building. Clearly account should be taken of the layman's assessment of what constitutes structural failure.
2. It could be reduced or eliminated by designing selected walls as structural elements in reinforced concrete, or perhaps a stronger, higher quality, "structural " CHB.

On this last point, it is the author's observation that the reinforced concrete structures of the 50's and 60's fared noticeably better than the more recent buildings of reinforced concrete frame and blockwork infill. Is it not time to take note of this and incorporate reinforced concrete in selected locations? This will make the performance of the building more predictable and will protect the remaining blockwork elements from damage. Yes, it may mean designing for a higher seismic coefficient, but one which more closely matches reality than the assumption of a fully ductile frame which is presently made. For most buildings the additional cost will be negligible. The benefits brought will be immense.

In summary, we must all remember that:

It is the earthquake and the principles of mechanics which determine which are structural and which are non-structural elements.

High Rise Buildings

The above comments relate principally to low-rise buildings where separation of CHB partitions from the frame is impractical since economical shear walls can be incorporated Oh easily. For high-rise buildings there may be significant additional costs associated with shear F walls. In such cases, it is vital that the CHB partitions are separated from the structural frame F so that they do not adversely affect the structural performance. This requires very close and t early cooperation between architect and engineer.

D. Construction Practices and Supervision

There is considerable evidence that close attention by designers and owners needs to be paid to ensure that construction matches the drawings. Furthermore, contractual specifications need to allow for changes to be made to take account of site conditions.

As a simple example, most drawings show stirrups and ties with 135 bends. By contrast, on site 135 bends are rare. The 90 bends are ineffective for confinement of the concrete core, resulting in a dramatic loss of potential strength and ductility.

Tighter control together with instruction and training of site foremen as to the importance of these details would assist in seeing the designers intentions achieved. The Philippine Chapter of the American Concrete Institute is about to launch a series of seminars aimed at helping site personnel understand the designer's intentions.

A feature of the ERP is the number of projects involving strengthening of existing buildings. Most designers recognize the need for careful investigation of the existing structure prior to finalizing the design of the strengthening work. But close supervision of construction is also vital in these projects. Exposure of the original structural fabric always brings surprises which require the design engineer to modify original design intentions to suit. She/he must be on site frequently throughout the construction phase.

Few people involved in structural design and construction would argue with this, but building owners are frequently hard to convince that the expense of retaining the engineer during construction is worthwhile. And yet at small cost they protect their investments whole building.

E. Bridges

One of the most striking features of the July 16 earthquake was the number of failed bridges. Those with discontinuous spans stood out. The disruption caused by even minor damage must serve as a reminder to all engineers to pay special attention to all aspects bridge design.

This includes:

Site Selection

Soil and hydrological characteristics are the main determinants. Both economy and the safety of the bridge warrant thorough investigation and comparison of options, costs, and risks before detailed analysis and design is commenced.

In the case of the bridges damaged in the July 16 earthquake, due account must be taken of the possible revised siltation regime due to earthquake-induced landslides in the mountains.

Proper site selection can result in greatly reduced risk, providing a worthwhile payback on the effort involved.

Foundation Design

Experience on the ERP suggests that investigation of the soil properties and the review of their implications are not as thorough or as commonplace as in other countries. An unfortunate drawback of the AASHTO Code used in the Philippines is its lack of emphasis on the substructure in developing realistic models for analysis. A bridge must be thought of as a single entity, with proper account taken of the interaction of the substructure (usually piles), the superstructure (piers and deck) and the soils down to bedrock.

Deck Continuity

Continuity of bridge decks is the single most important factor in earthquake resistant design. This goes beyond simply retrofitting links between spans. It should be built into the design concept.

The disadvantages of discrete spans were dramatically emphasized by the July 16 earthquake. And yet, design practices in the Philippines appear to have altered little. It is important that a review of "standard" designs is made with this in mind so that continuous bridge decks become the rule rather than the exception. Any delay in making this change may be regretted.

The Design Guidelines for the ERP Projects emphasize the above points.

F. Soil Condition
 
Many public buildings in the Philippines are built to standard designs prepared by MPWH, DOH and other agencies. The July 16 earthquake brought many examples of failure gf foundation soils, not just in Dagupan. This has brought a greater awareness by many engineers and owners of the need to carry out appropriate soils investigations as input to foundation design. Nevertheless some of the engineers on the ERP have argued that soil 0 investigations are "not necessary for single storey buildings". This statement appears to ignore the overwhelming evidence of the July 16 earthquake where many hundreds of single storey school buildings failed due to soil liquefaction. This is surely reason enough to spend a small sum on simple investigations and on modifying the standard foundations to suit.

Performing a soils investigation is but the first step. The results must be used to come up with an acceptably safe and economical foundation design. There should be no embarrassment among engineers if this process takes time and causes debate or delay. Every peso spent on a superstructure supported on a risky foundation is potentially a peso wasted.

G. Seismic Risk Data

There are two basic types of data which can be used to improve seismic resistant design:

1. Data on overall seismicity of the country i.e. the nature of earthquake shaking according to location, soil types etc.
2. Data which correlate building performance with known ground motions.

The ERP objectives include provision to improve the available data on both aspects.

One of the most important aspects of such work is to better define the variation in ground shaking with location (i.e. soil type and geology).

It could be argued that effort on seismic risk data is less important than the more fundamental issues covered above. This is almost certainly true in the short to medium term. But data gathering and related research should start now to ensure that it is available in useful form when designers can make use of the variation of risk and soil response in designing safer yet more economical structures.

 

WHAT OF THE FUTURE?

The earthquake of July 16 was undoubtedly the major seismic event of 1990. The major seismic event in 1991 was the issue of a new Association of Structural Enginners in the Philippines (ASEP) Guide. Although detailed code requirements did not change fundamentals, the seismic provisions are no longer relegated to an Appendix. More importantly, local engineers have written a special introduction to Earthquake Resistant Design for this guide. This is well written and covers all major issues. It is well illustrated and presented. All those involved in earthquake resistant design should take it to heart and commit  themselves to its principles. A commitment to see that its principles are applied will see a major advance in standards of earthquake resistant design in the Philippines.

The Introduction to the ASEP Guide covers all relevant aspects. Some examples are worth highligting.

Sec. 1.5.1 Demands of Earthquake Motion

Seismic design concepts must consider building proportions and details for their ductility(capacity to yield) and reserve energy-absorption capacity for surviving the inelastic deformation that would from a maximum expected earthquake. Special attention must also paid to connections which hold the force-resisting elemens together.

Sec. 1.5.3 Response of Elements Attached to the Building

Elements attached to the floors of the building (mechanical equipment,piping, non-structural partitions, etc.) respond to the floor motion in much  the same manner that the building responds to ground motion. However, the floor motion may vary substantially from the ground motion.

But elements that are flexible and periods close to any of the predominant modes of the building vibration will experince forces in a proportion substantially greater than the forces on the structure.

Sec. 1.6 Characteristics of Materials

In adopting the  philosophy of a ductile  structure behavior, the 1988 SEAOC Code thus requires smaller lateral forces that an elastic dynamic analysis would indicate.

Severe stiffness degradation is exhibit in Fig. 1.6 (f) masonry walls. this is one aspect which must be considered by structural engineers when incorporating this material in a structure.

Sec. 1.7.1.2 Design Provisions

The seismic  design provisions are minimum requirements and emphasis must be placed on structural concepts and detailing techniques as well as on stress calculations.

Sec. 1.7.3 Selection of  Stuctural System

It is  of utmost importance that careful professional scrutiny be given to the design at the  inception of the design as well  as at all significant stages ofdesign development.

1.7.3.3 Planning Concepts

Participaton of all the disciplines of the design team in the conceptual planning and selection of basic construction materials will ensure the optimaldesign at lowest construction cost and minimize the total design effort.

(A reference to achieving the most cost-effective sesimic resitance may have been better salesmanship-owners want value for money in the finished product).

Sec. 1.7.4 Techniques of Seismic Design

1.7.4.1 Layout

It is most desirable to consider the effect of the lateral forces on the structural system from teh start of the layout since this may save considerable time and money without detracting significantly from the usefulness or appearance  of the building.

1.7.4.1.1 Structural Form

Since the structural form is so critical in the response of the structur e of the earthquake motion, it is essential taht the structural engineer should be involved by the architect from the very beginning even at the schematic stage of architectural design involving the arrangement of spaces of the building.

Although contemporary structural analysis programs permit the study of complex structural model, these nevertheless are simplified abstractions of the real structure. Thus, not all characteristics can be included in the model. The more complex the structure, the greater is the responsibility of a less  reliable model.

1.7.4.1.2 Structural Symmetry

Asymmetry caused by the eccentric location of lateral force-resisting elements,e.g.,a building that has a flexible front because of large openings and an essentially stiff (solid) rear wall, can usually be avoided by better conceptual planning.

1.7.4.2.2  Shear wall construction is an excellent method of bracing buildings to limit damage, and this type of construction is normally economically feasible up to about 8 stories.

And to conclude:

1.7.4.2.3

The design engineer must be aware that a building does not merely consist of a summation of parts such as walls, columns, trusses, and similar components but is a complete integrated system or unit which has its own properties with respect to lateral force respose. The designer must follow the forces through teh structure into the ground and make sure  that every connection along the path of stress s adequate to maintain the integrity of  the system. It is necessary to keep in mind that the real forces involved are not static but dyamic; are usually erratically cyclic and repetitive; and can cause the deformations as well beyond those determined from the elastic design.

Nothing more needs to be said (or written). Those responsible fro the ASEP Guide are to be congratulated producing a landmark document. There is, however room for  more commitment to applying the principles. Every structural engineer should have a copy.

 

RECOMMENDED FUTURE DEVELOPMENT

Based on experince with the ERP, the following recommendations are made.

1. Surviving Buildings

Study them with a view to developing some empherical design rules which work. This has been done in other country.

2. Masonry

Research and develop techniques to provide reliable (and conservative) design criteria. Improve quality and quality control.

It is hoped that ASEP will lead the way in achieving this.

3. Standard Design

Review all standard design for public infrastructure components, so that they fir the best principles of seismic resistant design. Promulgate them widely so taht the old design  phased out quickly.

4. Education and Training

Instigate an intense series of seminars to promote teh ASEP Guide and particularly its principles. Place due emphasis on these principles in all underraduate courses.

5. Architechtural Awareness

Encourage architects to become  more aware of seismic resitant design. This is a welcome trend in USA, New Zealand and elsewhere. Both professions recognize the need to work together against the threat of earthquake damage.

6. Structural Features Reports

Appendix B is a form used in the ERP for designers to record the relevant structural features of each building. It is based on similar form used by the former New Zealand Ministry of Works and Development, used to assist in the approval of Public Building design in New Zealand.

It is strongly suggested that all structural engineers involved in buildings of significant size whether public or private, adopt( and adapt) Appendix B as a means of recording basic design assumptions. The discipline of filling the various sections is well worthwhile, and properly completed form is invaluable when referring back months or even years later.

7. Some Key Points

In a previous paper, a Table was presented summarizing some of the amin points requiring attention in the planning, conceptual, design and construction phases of building, bridge and roading projects. these remains very relevant and are reproduced as Appendix C.

 

ACKNOWLEDGEMENT

The permission of DPWH to present this paper, and the support of DPWH staff in its compilation is greatfully acknowledged. the views expressed are those of the author and should not be construed as being those of DPWH.

 

REFERENCES

1. ASEP Guide - Earthquake Resistant Design of Structures. 1991. Manila: Association of Structural Engineers of the Philippines.
2. "The Philippines Earthquake of July 16, 1990. Report on Field Visit by NZNSEE
    Reconnaissance   Team". Bulletin NZ National Society fro Earthquake Engineering, Vol. 24,  No. 1, March 1991.
3. Bridge Manual: Design and Evaluation. In Press. N. Z. 1991.
4. EERI. 1991. The Luzon, Philippines Earthquake of July 16,1990. Ca.:Earthquake Engineering Research Institute.
5. NZNSEE Reconnaissance Team, 1991. The Philippine Earthqauke of July 16,1990. Bulletin NZ National Society for Earthquake Engineering. 24(1).
6. Philippine Earthquake Reconnaissance Report. 1991. Earthquake Spectra. Supplement A.
7. U.K. Earthquake Engineering Field Investigation Team, 1991. The Luzon, Philippines Earthquake of 1990, U. K. Institution of Structural Engineers.

Ricardo M. Zarco*, Jose Tiburcio S. Nicolas*, Mario J. Aguja*
Arturo S. Daag** and Anabelle F. Ringor**
*University of the Philippines
**Philippine Institute of Volcanology and Seismology

 

INTRODUCTION

Animals may be able to anticipate strong earthquakes. The magnitude 7.8 July 16,1990 Luzon earthquake provided the opportunity to investigate this phenomenon amidst the suffering it brought. The task of this research is to quantify or measure some aspects of animal behavior, to assess the pragmatic value of this phenomenon as an auxiliary short term earthquake predictor.

Examples of these types of behavior include dog howling, excitability of animals in cages, cockroach swarms and other odd behavior. It is these types of behavior prior to the July 16 earthquake which are referred to as premonitory animal behavior.

Research in the People's Republic of China (PROC) has consistently shown the association of premonitory animal behavior to ground rupture location (faultline, fracture zones) and proximity to the epicenter. The literature on the subject is not available in this country so it was thought best to conduct independent inquiry and see for ourselves if the Chinese findings are cross validated in the Philippine experience. The emphasis of this investigation is the development of a technique to measure intensity of precursory animal behavior in various localities where they are suspect to be highest and compare these values against a control group.

 

METHODOLOGY

1. Nature of the Study

This is a retrospective field study of premonitory animal behavior which caught the attention of human observers. A survey- interview of selected respondents is the procedure of data gathering. The number of recalled events is assumed to correlate with the actual number of events occurring in a given location. Events are relatively easy to recall but the exact day or date and time of the incidents are less easily recalled.

Animals may be our indicators, they are our precision instruments that pick up chemical and physical or of geologic stress as an earthquake draws near. Our human observers selected from the peasantry, housewives, and workers are assumed to report events objectively, and the role of the behavioral scientist is to gather and analyze the data for its pragmatic and science values.

2. Choosing the human observer

Adults are preferred. Residents who devote much of their time around the household and community are selected if they own or have several domestic animals like dogs, cats, pigs, chickens and if they had stayed home several days before and during the earthquake. Mental alertness and verbal fluency are necessary. The principle behind this selection process is to maximize objectivity, hence validity.

3. The Interview

The interview is structured. It asks the respondent to recall animal behavior immediately before the earthquake.

Initially, pretests showed problems of vagueness since the task of recall was too generalized. Respondents kept recounting events during and after the quake and excluded non domestic animals such as snakes, rats, crabs, earthworms, cockroaches, ants and the like. The interview schedule had to be edited twice to include a list of specific set of domestic and non domesticates which the subject is made to specifically respond to. This new procedure improved data gathering and scoring.

The enthusiasm and willingness of the observers to recount the earthquake episode is noted. Not a single refusal was encountered among the 218 respondents chosen.

4. The Research Design

The epicenter of the earthquake was at 15°42'N and 121°7'E near the town of Rizal (PHIVOLCS data). Towns surveyed are shown in Figure 1.

The ground rupture line across Nueva Ecija was surveyed. This task covered six villages in all. The intention of trying out our measure of intensity of precursory animal behavior was conducted on those villages to see how the values would compare against other areas like places away from the ground rupture line. Previous similar studies in the People's Republic of China (PROC) had shown that observations of unusual animal behavior follow ground rupture lines and fracture areas. If this is true for this recent earthquake then logically these six villages surveyed should reflect higher intensity coefficients than areas where the earthquake had lessened.

The second spatial exercise attempted to test for the effect of epicentrality on animal behavior. Towns and cities were selected at 20 kilometer intervals from the epicenter and surveyed. A total of seven (7) towns and cities were chosen for this exercise. These communities were purposely chosen away from the affected fault and toward the SW and the southern direction where the earthquake's effect had lessened. The distant communities from the fault and the epicenter served as our comparator or control group.

The design, therefore, involves the selection and classification of areas according to their location in relation to the epicenter and the affected faultline. The primary objective of the selection procedure is to identify the possible effect and interaction of epicentral and faultline factors on the ability of animals to perceive premonitory signals prior to the July 16 earthquake. If animals perceive tension signals as a result of the pressure exerted below the faultline, then, one may expect that reports of anomalous animal behavior would not vary significantly in areas located along the affected faultline. However, if such geologic signals are mainly a result of the tension produced below the epicenter one could expect a gradual decrease in the reportage of anomalous animal behavior as the distance from the epicenter is increased. On the other hand, if these geologic stress signals are a product of the interaction of both the tension produced near the epicenter and along the affected faultline, a nonlinear trend in the reportage of anomalous animal behavior may be expected. To test these possibilities, areas were classified into four (4) major groups - those located along the fault and nearthe epicenter, those located along the faultbut moderately distant from the epicenter, those located outside the faultline and moderately distant from the epicenter, and those which are comparatively both distant to the epicenter and the affected rupture line (see Table lb).

5. The Concept of the Coefficients of Intensity

To quantify premonitory animal behavior, an area, or location is chosen. This is the unit of analysis, e.g. a village on a ground rupture line, or a town nearest the epicenter, or a distant city slightly affected by the earthquake. Residents, our human observers are selected for interview. They were asked to recall their observation as these occurred a week ( 7 days) before the earthquake.

Operationalized, the CI is location specific, covers a 7 day period, it is the mean value of observations per observer. This statistic can be accompanied by measures of variance, standard error, measures of peakedness and symmetry.

 

RESEARCH FINDINGS

Our data are presented in Tables 1a and 1b. Our analysis considered:

1. Spatial Factors and Quantification

Can the measurement technique on trial discriminate and explain coefficients of intensity between various areas in this study? Table 1b integrates an analytical design, a fourfold table. Let us now proceed with the analysis of Table 1b.

Cell I - Are those ground rupture line villages which are also elaicentral. Two factors (or variables) acting simultaneously on these three villages show the highest individual and group CT in the study.

Cell II - Are three towns nearest the epicenter, within a radius of 50 kms, but away from the ground rupture line. The mean CT shows the effect of epicentrality at its maximum level.

Cell III - The remaining three ground rupture villages which are farthest from the epicenter, The CT for this cluster represents the effect of location on a ground rupture line.

Cell IV - These four towns serve as our control group. They are beyond 50 kms. from the epicenter. Their CT indicate values of the less affected areas. Although they have very low values singly and collectively, the values do not approximate zero. To search for an absolute zero area it would require our team to select a location outside Luzon where the earthquake was not felt.

2. Anova

A one-way-analysis of variance of four cells or areas in Table 2 yields the following

1. The differentials of animal behavior intensity among the four groups (Cells) are statistically significant evidence by an F-ratio of 34.89, significant at 1%.

2. The subsequent multiple range test, known as the cheffe procedure, shows that the greatest differentials exists between epicentral (proximal versus distal locations. See tables 1b, 2, and 3.

3. Correlations

Another analytical method is to run test to see if the measurement technique reflects correlations between these two variables namely (1) the respondents' number of recalled precursory animal behavior events versus (2) distance from the epicenter. As a trial for correlations, a linear format was used. The six ground rupture villages with an N=76 showed an r=0.202 significant at 5% suggesting a slightly inverse relationship between distance from the epicenter and the coefficient of intensity. The second spatial design involves communities away from the faultline at approximately 20 km interval from the epicenter. With a total of 142 respondents frozen seven villages/communities, the linear correlation coefficient computed at -0.4 was likewise significant at 5%.

The pattern of the association between these two variables however is not best described by using a linear correlation format. This is because residential distance to the epicenter is dichotomous-either very near car distant. For the second design, we had noted that after the 50th kilometer, the coefficients suddenly dropped to very low levels and remained there suggestive of a plateau. o a point biserial format was used. The three fauitline villages within the 10 km radius from the epicenter were grouped against the other three fauitline villages with distances of more than 20 km from the epicenter. On the other hand, the three villages/communities away from the faultline between 20 to 50 km radius from the epicenter were grouped against those with other four communities with distances between 70 to 122 km from the epicenter. The results are:

Six villages located on the ground rupture line,

rpbi=0.213, significant at 1%

Communities staggered at 20 km interval from the epicenter,

rpbi=0.53, significant at 0.005%

These correlation coefficients are indicators of construct validity.

4. Stepwise Multiple Regression Analysis
What determines a respondent's number of observations reported upon an interview? We had wanted to answer this question early in our study to see if we were getting artifact. This is another validity inquiry. To answer this question, a multiple regression analysis was conducted. This statistical exercise is a multivariate technique which could indicate cause and effect relationship. Our dependent variable (the effect) is the human observer's productivity recalling premonitory animal behavior events upon interview. The independent variables, the multiple causes, are a host of factors like the geo-seismic characteristics of the environment such as residence on a faultline village, distance from epicenter; personal demographic characteristics of the respondent like the age, and the number of earthquakes previously experienced; and a cultural environmental characteristic - variety of animials owned or tended or found in the household.

The findings are gratifying. The major factor (variable) which determines the human observer's productivity to recalled events upon interview is proximity or location of his residence to the group rupture line. This accounts for 2510 of his productivity. The second factor is his cultural environment or the variety of animals in the household. This adds four percent more to the 25 raising the total to 2910. The three remaining variables practically contribute nothing to the equation. These are age, number of previous earthquakes experienced and distance of residence to epicenter.

It is the geoseismic character of the environment that excites animals to odd behavior, this in turn affects a variety of animals nearby and the human observer witnesses these events depending on the number of different animals around him. These are the bases of reported observations. See Tables 4 and 5.

5. The Temporal Dimension
The exact time when animals were observed to behave strangely is not an easy task to document. Respondents can easily recall and recount those events but when asked to specify time and dates, get confused. This is not a validity problem. It is a reliability deficiency. Very few of our respondents knew that animals presaged earthquakes. Only around 2 percent did before 16 July. The absence of a cognitive and belief system of this phenomenonmay explain the people's disinterest to remember the exact dates when animal events happened. Recalled events ranging :from one to three days before usually poses no problem. Four to five is a good estimate, six to seven days is a guess. Our data should be viewed with this limitation.

Two measurements were employed to gain insight on the temporal dimension of unusual animal behavior, namely, its onset and its magnitude. The first measurement attempted to determine how early animals act strangely before the quake. This was determined by recording the first time respondents noted abnormal animal behavior. On the other hand, measurement of the magnitude of unusual animal activity sought to reflect the frequency of unusual animal behavior as the day of the earthquake approaches. The basic difference of these two measurements is the recording of recurrent observations. In the measurement of onset, recurrent unusual animal activities were recorded only once, while in the measurement of magnitude recurrent behavior were recorded as these occurred.

When do animals begin to elicit unusual activity? Practically all observations, except for one case, were within a seven day range. Pooling all reports, a temporal pattern emerges. The onset of animal excitability is a U curve of a week's duration. The first observations start with a high frequency at seven days before the earthquake. This is followed by a drop to lower frequencies until the fifth day before, then surges on two days before until it reaches the peak level on the day of the earthquake. The most numerous reports build up to one to two hours before the main shock (See Tables 7, 8 and 9).

The cumulative reports (magnitude) of premonitory animal behavior actually increases daily up to the day of the main shock. The observed reports surge two days before and on the day of the main shock. The most numerous reports build up one to two hours before the main shock (See Table 10).

The pioneers of the studies on animals and earthquakes from the Institute of Biophysics of the Academia Sinica have reported in summary that anomalous animal behavior reaches modal values within one day before the earthquake. Professor Jiang-Jin-Chaing of the Academia Sinica writes:

1. The analysis of data collected after many earthquakes shows that most of the anomalous animal behavior occur within one day before the earthquake.

2. The analysis of 201 cases of abnormal animal behavior shows that most of them occur within 11 hours and increase sharply 2-3 hours before the earthquake. The mean appearing time of the anomaly and the standard deviation, respectively, equal to 2.7 and 2.5 hours. So, we suppose that the unusual behavior of animals is possibly a short term macroscopic premonitory phenomenon of earthquakes.

Our findings differ from China's. Our temporal pattern, the frequency of premonitory animal behavior by days before the earthquake have a much longer lead time, meaning that the reported observations occur much earlier, by at least six days. At quick glance we find the temporal pattern uniform in the four areas or groups (cells) except for one slight exception: those six (6) villages located on the ground rupture line (fault) pooled together and compared to the rest of the communities in this study revealed a slightly shorter mean lead time for the six villages. The differential of only .69 days is slight but significant at the 5% level. See Table 6.

We have no ready explanation for these disparities between our temporal pattern add Beijing's, as well as the slight differential s a possible tunction of location. Our study on animals and earthquake is limited only to the 16 July Luzon earthquake. We still are hesitant to speculate can the possible association between location or spatial versus ternprrrl factors, versus magnitude, of earthquake. We need rnore earthquakes to study in the local scene.

6. Precuisory Animal Behavior
The most reported animals are dogs, chickens, and cockroaches,

The ring is the most mentioned animal in this study. Being ubiquitous, overt, and the bet understood, owners are apt to take notice if activity deviates from baseline, normal level. Dogs are reported to bay (howl) repeatedly day after day until the earthquake occurs. Whining, jumping crazily, scratching the floor or the ground, and refusing eat. Older and
more mature dogs signal these overt acts. Young ones and puppies as a general rule do not. Dogs however react similarly to other geophysical events and to rabies. Filipinos also restrain, suppress their dogs when they bay since this is interpreted as omen of impending death. Dogs are sometimes killed by their owners on the belief that the threat is averted if warnings stops. Baying dogs, being audible and overt, are the most mentioned event. This behavior involves the observer's dog or a neighbor's dog within sight, or dogs heard baying in the distance, out of sight.

Chickens come second. When kept in coops the reported behavior is restlessness, When allowed to freely roam, they stay on rooftops and trees where they normally roost for the night and do not come down despite the late hour. Chickens abound in rural areas and decrease with urbanization. About half of the described behavior is recurrent, repeated, days before the earthquake.

Cockroach swarms rank third. This pest has its utility. Emerging from crevices the colony surges out in panic, some flying others scamper in different directions. "Roach swarms" are to be differentiated from cockroaches feeding in large number in dirty surroundings at night. Cockroaches are ubiquitous but a swarming occurs only once per colony. This event is of very short duration. Because of its non repetitive nature, the event could easily pass unnoticed. Roach swarms are under reported. Many observers who witness these events are mostly not aware that this is a premonitory sign of an earthquake.

Like cockroaches, snakes, river crabs, rats and even termites (winged ants) are reported to have emerged from their burrows and were sighted in greater number, days before the quake. Fish jumps, fish kills have been reported. In China the premonitory activity of water fowl like ducks and geese is to stay away from the water. We have no reports of these events since areas surveyed did not have enough domestic waterfowl.

Larger animals like pigs when cooped show excitement and the desire to break out. Water buffaloes are described to manifest strange postural acts.

7. Narrative examples of reported premonitory animal behavior.

1. Miss Clarita De Leon, 48 years old, housekeeper, and a resident of Poblacion Rizal, Nueva Ecija observed their dog bayed two hours before the earthquake on July 16, 1990. She likewise noticed their cattle bellowed a day before the quake.

2. Mr. Florencio Ruiz, 70 years old and retired army serviceman, tends pigs, chickens and cat in their home in Rizal, N.E. He noticed his chickens in cages were restless for seven days before the quake especially at night without apparent reason. His pigs were likewise restless during the same period. Their cats, which normally stay in the house were afraid to go inside four days before the quake.

3. Mr. Reynaldo Bauto, a 45 year old farmer from Poblacion Rizal, Nueva Ecija, heard his dog bayed two hours before the July 16 quake. However, he did not notice any unusual behavior among his other animals (pigs, carabaos, and chickens).

4. Mr. Rodrigo Lucero, 45 years old, and a resident of Macapsing, Rizal, Nueva Ecija tends pigs, a dog and a cat. He noticed his dog bayed and barked restlessly for three consecutive afternoons (3PM) before July 16. He was puzzled why his cat was restless and kept on moving inside their house for two afternoons before the quake.

5. Ms. Correon Cabangay, 30 years old and a resident of Macapsing, Rizal tends several animals (dogs, pigs, carabaos, and chickens). She reported observing their pigs as losing appetite. for seven consecutive days before the quake. Although their dog did not howl, she heard the dog of their neighbor howling for three, nights before. She was also surprised to see a large number of cockroaches swarm in their house that afternoon, two days before the quake.

6. Ms. Rebecca Antonio, a 43 year old housewife from Macapsing, Rizal, N.E., heard their dog bayed and barked restlessly for three nights before the quake.

7. Mr. Juan Villanueva, a 56 year old farmer from Macapsing, Rizal noticed his pigs were restless without any apparent cause two mornings before 16 July. The night before the quake, he also observed his cat as if afraid of something. Cockroaches swarmed into their house that night. On the morning of July 16, his carabaos and chicken became excited and restless.

8. Mang Benito, 65 years old, tends pigs, carabaos, chickens, and dogs. In the morning of July 15, he saw and heard their cattle mooing facing the "cast" (location of the faultline) for 10 minutes. The following morning, his dogs howled and his pigs became restless. He is one of the respondents who believe that animals presage earthquakes long before this recent one. He remembered seeing and hearing a carabao bellowing before the earthquake which flattened Ruby Tower. This occurred 22 years ago.

9. A 6 year old farmer from Bagting, Gabaldon, N.E. was awakened when his dog howled and his chickens cackled at 1:00 AM of July 16. His neighbor°s dog also bayed, fie also heard his neighbors' chickens cackling excitedly. They were having a drink in the yard of a friend's house in that afternoon of July 16 when he went to the toilet, he was surprised to see a large number of cockroaches scampering as if looking for a way out.

10. Ms. Marilou Martin, a 30 year old resident of Palayan City, reported that their dog howled for seven consecutive evenings before the July 16 quake. Also, their chickens became restless on the evening of July 1.0 without any apparent cause.

 

CONCLUSION

From the findings of the study and what is already scientifically known can this topic, pragmatic technique using animal anomalies gas a short term earthquake predictor should be put on trial use on some sections of the Philippine fault line which earth scientists believe will experience a strong earthquake in the next few years to come.

Only o percent (2%) of respondents in or study new that animals pressed earthquakes, so it could be said that ninety- eight percent (%) of the population are ignorant of the phenomenon. This implies above all a prerequisite task, an information-educa tional program on animals and earthquakes directed at adults residing in high earthquake risk areas and school teachers, for multiplier effect, so that they would be sensitized and be more observant of animal behavior and learn to discern those forms which presage tectonic, earthquakes.

if this pragmatic technique is tested in rural villages and small isolated areas, the judgmental task of earthquake prediction becomes also the responsibility of residents of these communities. This leaves the tasks of evaluation, research, dissemination of prediction techniques to the PHIVOLCS, the country's highest authority on volcanoes and earthquakes.

 

REFERENCES

Adams, R.D. 1976. TheHaicheng China Earthquake of 04 February, 1975: The First Successfully Predicted Earthquake. Bulletin of the New Zealand National Society for Earthquake Engineering: 9(1).

Amin, E., R. Tabanlar, and F. delos Reyes, 1990, Earthquake Information Bulletin No. 2. dated 9:15 M (DST) 7-17-90, Philippine Institute of Volcanology and Seismology, Hizon Bldg. 29 Quezon Avenue, Quezon City. (This is the official bulletin of the Philippine Government on the July 16, 1990 earthquake).

Delos Santos, Felix. 19911. Animal Behavior Strangely before the quake. Phillipine Star. July 30, 1990.

Doyo, Ma. Ceres . Who's Sister Emma? Philippine Daily Inquirer. Sept. 5, 1991.

Hamilton, Robert M. 1975. Earthquake Studies in China. Earthquake Information Buletin.7(6).

Jiang Jin-Chang and Liu Xiang-gun. Undated. A Study of the Relation Between Acoustic Emission and Animal Unusual Behavior Prior to Earthquakes. Beijing: Institute of Biophysics, Academia Sinica.

Lowry, M.A. 1982. Can Animals help Earthquake Predictors? New Zealand Vet. Journal 31: 35-39.

Ma Jing-sheng and Jiang Jin-chang. Undated. Ordinal Characteristics of Animal Unusual Behavior Prior to Earthquakes and Its Analysis: Institute of Biophysics, Academia Sinica.

Mead, Dale. 1976. How the Chinese Predict Earthquakes. Science Digest.

Newhall, C.G., R.V. Sharp, G.E. Wieczosek, L. Wennerberg, and J. Bicknell. 1990. Final Report on the July 16, 1990 Luzon Earthquake. US Geological Survey, Philippine Institute of Volcanology and Seismology with support from U.S. Agency for International Development Office of Foreign Disaster Assistance October 29,1990.

Ramos, Emmanuel G. 1982. Personal communication on earthquake prediction

Reasenberg, Paul. 1978. Unusual Animal Behavior Before Earthquakes. Earthquake Information Bulletin. 10(2).

Rous, Alberto T. Science Unravels Animal Behavior during Quakes. Philippine Journal. November 13,1989.

Simon, Ruth B.1975. Animal Behavior and Earthquakes. Earthquake Information Bulletin. 7(6).

Wong, T.P. 1976. Earthquake Forecasting. Hongkong: Tenshai Publishing Corp., 106 p,

Zarco, R.M. and PHIVOLCS Research Staff. 1986. Anticipation Reaction and Consequences: A Case Study of the September 1984 Mayon Volcano Eruption. Q.C.: PHIVOLCS. 21 p.

__________. 1976. Conference Papers on Abnormal Animal Behavior Prior to Earthquakes held at Menlo Park 345 Middlefced Road, California, on October 23-24, 1976. U.S. Geological Survey.

__________. 1979. Conference Papers on Abnormal Animal Behavior Prior to Earthquakes. Second Conference held in Galveston, Texas, October 18-19, 1979.

__________. 1977. Animals and Earthquake, Earthquake Group of the Institute of Biophysics, Academia Sinica. Beijing: Seismological Press.

__________. 1991. Howling Dogs Save Imperiled Sta. Rita Folks. Philippine Daily Inquirer. Aug. 25, 1991.

__________. Some General Information on Earthquakes. Prepared by the Seismology Department, Manila Observatory, Ateneo University, Quezon City, mimeographed undated document.

Raoul M. Cola
College of Public Administration
University of the Philippines

 

ABSTRACT

During the 16 July 1990 earthquake, households and communities immediately responded to its Impact to ensure their survival and the restoration of their former lifeways. The response mainly made use of available resources (material and non-material) and group (kinship, neighborhood or community based) effort. However, the response was conceived and implemented in a haphazard and trial-and-error manner.

One of the source of divisive competition and conflicts at that time was the absence of defined procedures for households in assistance procurement. Although initially they relied on their community leaders who secured assistance from various government and non-government sources, many households preempted their leaders and other households by directly soliciting assistance outside their communities. Government and non-government units based outside the community failed to respond immediately to the situation.

Communities evolved a distribution system of relief assistance based on their own concept of fairness. This distribution system had built-in accountability procedures so that short-cutting it invited suspicion of pilferage. But instead of working within this system, some government and non-government units directly delivered relief goods to the households. Doing so upset the functioning of the existing distribution system and resulted to a number of undesirable consequences.

In the absence of outside assistance, the survival and the normalization of the lives of the households and their community hinged not only on the household (such as houses) and community (such as roads) properties spared by the disaster but also on their natural resources. As a result of the breakdown of the distribution system of goods and services, the households became more dependent on the resources in their natural environment. The communities who had these resources and knew how to use these had greater chances of surviving the disaster even without any outside assistance.

It is apparent that any effective natural disaster mitigation program should be built around the community rather than on higher government units and on non-government units. The effort of these units should only supplement rather than supplant that of the community. Making the community the centerpiece of a disaster mitigation program is borne out of the realization that government and non-government units, particularly in the developing countries, have very limited capability to assist afected communities. Given the poverty prevailing in developing countries, outside assistance if given outside the context of the concept of self-help, readily nurtures dependency among affected communities by supplanting local capability.

 

INTRODUCTION

The impact of the twin earthquakes in Northern Luzon last 16 June 1990 and the manner the government response was organized brought into focus the urgent need to formulate a systematic disaster preparedness and mitigation measures. The measures are aimed at reducing not only the risk ref disaster but also the duration and scope of its impact. The need for such measures has long been felt because of the high vulnerability of the Country to natural disaster. It ranked second as having the most number of such disasters between 1960 and 1981 among 53 countries surveyed1 . These countries had an average of one disaster per year white the Philippines had four, for each disaster, the Philippines lost an average of 203 human lives and an unestimated cost to the economy.

Although the physical event comprising the disaster cannot be prevented, its impact call be minimized by disaster preparedness and mitigation measures. However, such measures have to be based on two types of research-based information: the nature of the physical event spurring the disaster and the human behavior related to the disaster, This study is carried out to contribute to the provision of information of the letter type2. It captures aspects of' the disaster-related behavior of residents in the earthquake affected areas as seen in two settings -- in the household and in the community. This behavior is reviewed and lessons which may serve as input in the preparation of a disaster preparedness and mitigation plan are subsequently drawn.

 

OBJECTIVE OF THE STUDY

The objective of the study is to know how the residents in Northern Luzon reacted to the impact of the earthquake both as members of the household and the community. To pursue such objective, the study will to answer the following questions:

1. What was the level of awareness of the residents with regards to the geologic hazards in their communities?
   

2. What actions did the residents take at the household and community levels to cope with the impact of these hazards when these occurred?
   

3. What household and community resources were tapped to cope with such impact and how were these used?
   

4. What types of assistance were sought by the residents from outside their household and community and how were these secured and distributed?

To answer these questions, the study reconstructs the strategies implemented by the households and communities to ensure their survival in a disaster situation and to hasten the normalization of their day-to-day living patterns. The reconstruction enables the study to identify the effects of each strategy and the problems encountered in their implementation. In consideration of these effects and problems, the study sorts out these strategies which worked and should serve as basis for a household and community-based disaster preparedness and mitigation measures.

 

METHODOLOGY

The study used two main data collection strategies: sample survey and key informant interview. The survey was conducted among the households in the provinces of Benguet, La Union and Pangasinan where the earthquake registered at intensity 8.0 at the Modified Rossi-Forel Scale. The sample size was drawn using a multi-stage sampling design. From said provinces, the study randomly selected the sample cities and towns from where the sample barangays were subsequently taken. There were two sample cities and five sample towns. The two sample cities were Baguio of Benguet and Dagupan of Pangasinan. The sample towns were the following: La Trinidad of Benguet, Agoo and Aringay of La Union, and Calasio and Malasiqui of Pangasinan.

From the cities, 30 sample barangays were drawn and from the towns, 22 barangays. From a total of 52 barangays, 109 sample households were taken and were distributed as follows: 53 city households (40 in Baguio and 13 in Dagupan) and 56 town households (22 from urban and 34 from rural barangays). The sample size, from towns and cities to the households, was determined at 95 percent reliability with maximum sampling error of 10 percent.

The study conducted in-depth interviews in the 48 sample barangays. The interviews were administered to barangay leaders and other persons who were key participants in community activities undertaken to ensure the well-being of the members in a disaster situation. A set of questions was prepared beforehand to guide the interviews.

 

SITE OF THE STUDY

The study site is located in the northwestern part of Luzon Island at approximately 15° 5' latitude in the North and 120° 5' longitude in the East (Fig. 1). It covers three adjacent provinces with varying topographic and geologic characteristics. Because of these physical variations, different geologic hazards were created by the earthquake. There were landslides in Benguet and parallel and subparallel ruptures in La Union and Pangasinan. In some areas of Pangasinan, liquefaction took place. Being a densely populated area, these geologic hazards threatened so many lives.

The 1990 population density in the three provinces was 303 persons per square kilometer while the national density was only 202 persons4. The population in cities was more dense than in the towns. Baguio City had 183,102 persons (3,744 per square kilometer) and Dagupan City had 122,247 persons (2,801 per square kilometer). The two cities combined had a population density of 3,300 persons per square kilometer. In contrast, the towns had an average population of 55,845 persons or a density of only 648 persons per square kilometer. Such density was 2,652 less than that of the cities but more than three times greater than the national density.

 

DISCUSSION OF RESULTS

Using the data gathered, the study reconstructs the situation during and immediately after the earthquake. The discussion covers the following aspects: awareness and outright response to the seismic hazard, impact of the earthquake and the survival strategies implemented at the household level, impact of the earthquake and community-based mitigating measures, mobilization of the household and community resources, and sourcing and sharing of external resources. From the discussion of each topic, the study culls the lessons which may serve as experience- based input to the preparation of a disaster preparedness and mitigation measures. Such input is part of the effort to come out with measures which are not only suited to the needs of the households and communities but also within their capability to put to work.

Awareness and Outright Response to the Seismic Hazard

The earthquake which struck Northern Luzon at 4:26 (Daylight Saving Time) in the afternoon of 16 July 1990 was never expected by the respondents. This was because 96 percent of them were fully unaware that their residence was located in an earthquake-prone area (Table 1). The very low level of awareness among the respondents on the geologic hazard in the area cuts across place of residence, income status, degree of mass media (radio and newspaper) exposure and frequency of attendance of community meetings.

Such awareness level is unlikely considering that the respondents had a high mass media exposure and frequently attended barangay meetings. Close to 95 percent of them owned a radio and listened to it almost daily (28 days a month). Half of them were regular newspaper readers although most of these readers were in the cities (71 percent) rather than in the towns (27 percent). However, there were more community meeting participants in the towns (89 percent) than in the cities (57 percent). This means that while in cities, the information provided by the radio was supplemented by the print media, in the towns, it was supplemented by community meetings. But whether in cities or in towns, the number of community meetings participated in by the respondents averaged only three times a year.

The very low awareness of the respondents on their seismic risk, despite their high mass media exposure and community meeting participation, points out one fact: the absence of a systematic effort to disseminate information on the physical hazards existing in the area. Such absence is further indicated by the source of information of the respondents who were aware that the area is a exposed to seismic risk. Half of them learned it from their old folks while the other half, from their neighbors. Because all sources are informal, none of them obtained the information from formal sources such as the mass media and public officials.

Being mostly unaware of the seismicity in the area, all the respondents were panic-stricken upon sensing the earthquake. The earthquake caught 82 percent of them indoors and 18 percent outdoors. Among those who were indoors, 71 percent were inside their houses. The rest were in their work places or some public buildings. They did not react to the earthquake in a similar manner: 57 percent ran somewhere and 43 percent stayed put. Most of those who ran wanted to get out from the enclosed structures where they were. However, those who were caught indoors reacted in almost the same way with 96 percent of them staying put in where they were. Being in their yards or in the farms or in the streets, they really had nowhere to run to. Except for one respondent, none of them reported a purposive reaction such as putting off the main electrical switch or moving under the door beam. The absence of such reactions merely indicates their lack of knowledge on the appropriate actions to be done in such a situation.

Impact of the Earthquake and Survival Strategies Implemented at the Household Level

The impact of the earthquake on man-made structures resulted to the disruption of the normal lives of the sample households. The extent of the disruption created is reflected in the problems confronting the households immediately after the earthquake. Nearly all the problems pertained to basic necessities: shelter, water, food, fuel, mobility, rescue services and income sources. Being basic necessities, the solutions to these problems meant the survival of the members of the households.

Need for Shelter and Its Solutions. The earthquake affected 84 percent of the houses of the sample households (Table 2). It indiscriminately wrecked houses regardless of its location and the owner's income status. The percentage of houses which were destroyed was about the same whether in the cities or towns (85 vs. 84 percent) and whether in the highland or lowland (82 vs. 86 percent). This indicates that the landslides in the highland (Benguet) was just as destructive as the ruptures and liquefaction in the lowlands ( Pangasinan and La Union). It also destroyed 83 percent of the houses of the rich and 84 percent of the poor. The rich were the ones earning more than P4,998 per month (average income of the sample households in 1989) while the poor were the ones earning less. However, the earthquake was more considerate to houses made of light than of durable materials. There were more houses made of bamboo, grass and palm leaves which withstood the impact of the earthquake than those made of cement and galvanized iron (67 vs. 88 percent).

Among the earthquake-affected hoses, 89 Percent were partially destroyed and 11 percent totally collapsed. The damage sustained by those which were partially destroyed ranged from cracks in the walls and floor (38 Percent) to collapse of certain parts of the, structure (7 percent). Some 1 Percent of the houses remained intact but were dislocated from their original position. The distribution of houses by type of damage sustained in cities was largely the same as that in towns. However, there were more houses in cities which totally collapsed than in the towns (15 vs. 7 percent). Part of the explanation was the fact that there were more houses made of durable materials in the cities than in the towns (91 vs. 70) percent).

Because of the damage on housing structures, the need for shelter was the most widespread problem that emerged immediately after the earthquake. Such need was reported by 50 percent of the sample households or 34 percent less than the percentage of those with damaged houses. One reason is that in spite of the damage, some houses were still deemed by the households safe for habitation. Another is that temporary shelter was easily provided by one's neighbor and relatives. Because the kinship network was stronger in towns than in cities, the need for shelter was confronted by more city than town residents (60 vs. 39 percent). In fact, 44 percent of those in need for shelter in the towns took refuge in their neighbors or relative's house but none did the same in the cities.

Instead, most city residents chose to either construct a temporary shelter (40 percent) or transfer to an evacuation area (34 percent). Only 17 percent of the town households did the former and 11 percent did the latter. Besides, many town households were hesitant to leave their houses for fear that it might be burglarized or their animals might get lost in their absence. Thus, those who evacuated either left one male member behind to watch their belongings or stayed in their house during the day and in the evacuation center during the night.

There were about the same percentage of households in cities (26 percent) and municipalities (28 percent) who repaired their houses right after the earthquake to make these households habitable. However, the restoration of houses for normal occupancy may take sometime because only 36 percent of the sample households did it six months after the earthquake. The restoration went faster in the cities where 47 percent of the households had already done it. In contrast, only 25 percent of the town did the same. The main factor behind the uneven rate of housing restoration was the cost. The average amount spent by those who had already restored their houses was P36,674. The cost was higher in the cities (P40,930) than in the towns (P25,625) but the earnings of the city households was three times of the earnings of town households (P7,450 vs. P2,452 per month). Moreover, the cities had more rich households than the towns (73 vs. 27 percent) just as the towns had more poor households than the cities. Because of their greater capability, there were more rich households who completed the restoration of their houses than poor households (56 vs. 30 percent).

The households who had not yet restored their damaged houses, likewise, pinpointed the cost as the reason. The average restoration cost of P36,674 was equivalent to a seven or eight months earnings of the sample households whose average income was P4,874 per month. Even the rich had to save their entire income for six months (P9,248 per month) to come up with the average restoration cost of their houses (P51,949). The houses of the poor households had much lower restoration cost (P6,125) representing only their three-month income (P2,182 per month). This lower cost was borne out by the lower cost they spent for housing materials and labor. Most materials which they used for the restoration of their houses were gathered from nearby brushland (timber, bamboo and thatch grass) and swampland (nipa leaves and mangrove timber). The labor was readily provided by their kinsmen and neighbors. By using the resources of their immediate environment and the capability of an informal workgroup, 1.5 percent of the poor households even managed to reconstruct their houses without any financial outlay.

Problems an Water, Food, Fuel, Mobility and Rescue Services and Their Solutions. The problems on water, food, fuel, mobility and rescue services were mainly a result of the breakdown of the network of private and public services as a result of the earthquake. The damage on water and electric plants, farms and factories, roads and ports, pipe and wire lines disconnected all the distribution systems which supported population centers and linked these centers to each other. Because basic necessities in cities and towns were largely provided by said network and its breakdown occurred at a time of emergency when its services were most needed, multiple problems were felt by the households.

The foremost of these was the shortage of water and food. Water was a problem of 49 percent of the sample households and food was a problem of 47 percent (Table 3). Both problems were felt more in the cities than in the towns. In cities, the households who were in need of water comprised 66 percent (vs. 32 percent. in towns) and those in need of food comprised 49 percent (vs. 45 percent in towns). There was a smaller percentage of town households who ran short of water because many of them were still using the, traditional sources such as piped and dug wells, springs and streams. Although the ground ruptures generated by the earthquake dried up car degraded some of these water sources, others remained undisturbed, In contrast, more city households drew their water from individual household connection provided by local water supply systems.

When the operation of these water supply systems was halted by the earthquake, 43 percent of the affected households looked to the traditional water sources as alternative. These water sources which became obsolete at the advent of the individual household connection were again put to use. Some households walked a kilometer or two to get to these sources. Where such sources were not available or no longer useful, 38 percent turned to rain which was abundant at that time being a monsoon season. They gathered rainwaters from rooftops or through plastic sheets. In city centers where there were no traditional water sources and rain water difficult to gather, the households exercised their claim-matting functions by nudging government authorities for water rations.

The percentage of households who felt the shortage of food did not widely vary between cities and towns. However, the nature of their problem varied. In the cities, there was a general scarcity of all kinds of food but in the towns, it was limited to certain food stuffs. The vegetable-growing households in Benguet mainly ran short of rice and fish while the fishing households in La Union were in need only of rice. The inland households of Pan- and La Union had enough rice but did not have fish, sugar and salt. To meet their need, 98 percent of the households sought it from various sources: relatives, neighbors, stores, community leaders, governmental and non-governmental agencies. The need for food was one problem which prompted most households to enlist outside assistance. This means that the problem was beyond their capability to solve. Only 2 percent of the sample households had stock of the necessary food stuff which they rationed for two days.

Smaller percentages of sample households encountered problems on fuel (34 percent), mobility (5 percent) and rescue services (3 percent). Like the need for shelter, water and food, the problems on fuel and mobility burdened more city than town households. The lack of fuel was felt by 45 percent of the city households but only 23 percent of the town households. Mobility was needed by 8 percent of the city households but only 2 percent of the town households. The higher percentage of city households with problems on fuel and transport again indicated their greater dependence on public utilities such as electricity and mass transport. The town households relied more on kerosene and firewoods for fuel. Their need for mobility was also minimal because their food requirement was not wholly provided by the market and their travel destinations were usually accessible by foot or by nonmotorized transport modes.

Nonetheless, most sample households handled the problems of fuel and mobility on their own. For fuel, 79 percent scoured for candles and firewoods or made kerosene lamps for lighting. Firewoods were also used for cooking in place of electricity and gas. The rest elevated the problem to their community. They worked with their community leaders for the restoration of electric power supply in their respective areas. Among those who were in need of transport, 94 percent learned to use their foot. The rest who were vehicle owners limited the use of their vehicles to emergency and vital errands.

There were few sample households (3 percent) with members who were injured by the earthquake or were missing. These households rushed the injured members to the nearby hospital with the assistance of their neighbors or monitored both radio and word-of-mouth reports to locate the missing members. Thus in both cases, the sample households mobilized themselves to solved their own problems.

Destruction of Income Sources and Its Solutions. Based on the income sources of the sample households, the economy of the study site can be considered highly diversified. But the main source was salaries and wages supporting 71 percent of the sample households (Table 4). The dependence of the city households on this income source was much greater than of the town households (97 vs. 64 percent). Although an average household in the study site had two income sources, the portion derived from salaries and wages composed 55 percent of their average income.

In cities, business was next to salaries and wages as the income source providing for most households while in the towns, it was farming. Business was an income source of 54 percent of the city households (vs. 26 percent in towns) and contributed 27 percent of their average income (vs. 23 percent in towns). Meanwhile, farming supported 39 percent of the town households (vs. 6 percent in cities) and accounted for 20 percent of their average income (vs. 1 percent in cities). Other income sources in the study sites were remittances, livestock and poultry, pensions, rentals from properties and fishing. The average household earned P4,998 per month in 1989 or higher than the 1988 national average of P3,36.4 4 in the rest of the country, city households earned more then the town households (P 7,450 vs. P2,452).

The earthquake put the economy of the study site at a standstill and disrupted the operation a f the income sources of 56 percent of the sample households, The percentage of households affected was greater in cities than in toms (63 vs. 49 percent, in the highland than in the lowland (77 vs. 44 percent) and among the rich households than among the poor (60 vs. 54 percent). In terms of income source, it hit most severely the households earning from salaries send wages, affecting 36 percent of them, More salary and wage earners suffered in cities than in towns (54 vs. 20 percent), indicating once again the greater vulnerability of urban centers tea the earthquake, The impact of the earthquake on the farming households was not as extensive with only 16 percent of them being affected. Households relying can other income sources were also affected but only to a small extent: 5 percent among livestock and poultry raisers and 6 percent among property lessors.

Nonetheless, the rehabilitation of tire work places of salary and wage earners seemed to be the most swift. Six months after the earthquake, 62 percent of the affected salary and wage earners were, already back to normal work. The rehabilitation of the work places of the rest of the affected wage and salary earners took more time due to the greater damage sustained, the higher cost of rehabilitation and the degree of effort exerted by those concerned. Most of these were in cities where only 54 percent of the salary and wage earners returned to normal work after six months. In towns where the percentage of affected salary and wage earners was smaller, 82 percent were already working under normal conditions after the same period.

The rehabilitation of farmlands was also relatively swift with 59 percent of the farming households back to normal operation after six months. The rehabilitation was again faster in the towns than in the cities. In towns, 66 percent of the farming households were already operating normally six months after the earthquake while in cities, only 40 percent did the same. Among the livestock and poultry raisers and among property lessors, less than half had normal operation after six months: 40 percent among livestock arid poultry raisers and 43 percent among property lessors.

However, only 13 percent of the affected households were involved in the rehabilitation of their income sources. None of those who did were salary and wage earners because they placed the entire burden of rehabilitating their work places on their employers. Having two income sources, the average household depended on the other source while waiting for the normalization of the operation of their work places. Those with only one income source put up small-scale business enterprises (such as vending and candy making) or secured loans to tide them over while still unemployed.

However, the farming households immediately cleared their land of boulders or drained it of flood waters one or two weeks after the earthquake and resumed cultivation. Those whose lots could not be immediately rehabilitated, farmed other portions of their lands. Two fishpond-owners restocked their ponds with fingerlings two weeks after the earthquake, spurted warm water and decimated all their fish stocks. But for some fishermen, the resumption of their livelihood generation activities were affected by the long-term effect of the earthquake. In Barangay Carael, Dagupan City, the fishermen reported of the sudden depletion of fish in the river. Two varieties of small shellfish (damisil and kakayat) were said to have proliferated and were consuming the algae which served as fish food.

Impact of the Earthquake and Community-based Mitigating Measures

The impact generated by the earthquake at the household level became a community concern when it turned out to have affected a considerable number of households and a common solution was sought out by these households. These solutions were worked out and implemented by the community through a cooperative effort between members and leaders. Existing community organizations usually served the catalyst of community mobilization. The diversity and creativity of the solutions varied in spite of the similarity of the problems.

Food Shortage and its Mitigating Measures. Among these problems which inspired community-level solutions was food shortage which swept through all the 46 communities covered by the study (Table 5). These communities solicited food relief from governmental and non-governmental agencies. This measure indicated that these communities have little food in reserve and needed outside assistance for contingency. Nonetheless, 11 communities ensured that such assistance was used in a manner considered most desirable by the community members by operating a communal kitchen. But in one community, the members themselves were the ones who contributed the food for the communal kitchen.

The community kitchen was managed either by entire community or by a neighborhood. In this kitchen, the donated food stuff was prepared by the community members and was subsequently distributed according to certain criteria agreed upon. This measure safeguarded the donated food stuff from pilferage and placed its manner of distribution above suspicion. The community kitchens operated for an average of four days. Afterwards, uncooked food was simply distributed to the individual households through a certain system. Contributing to the closure of the community kitchen was the mob of non-community members who requested for a share and reduced the amount of food for the community members. There was also a realization that a communal kitchen was difficult to maintain in communities with scattered housing distribution. This was because the community members found it too tedious to walk a certain distance to take their meals.

While all communities received food assistance from outside, some communities carried out measures which enabled its internal food distribution network to operate normally in a crisis situation. In 6 communities, arrangements were made with store owners to continue selling goods at pre-earthquake prices until their supply ran out. The stores which closed before its stock was depleted were reprimanded by the community members. In 3 of these communities, the stores were prohibited to jack up the prices of their wares. The members of 3 other communities pooled together some money and bought certain food items from wholesalers. In this manner, they obtained the food items at prices lower than those quoted by the retailers whowere their usual suppliers. Through such measure, the community spared itself from the sudden increases of prices which occurred immediately after the earthquake. In one community, the members through their leaders secured three-day credit from market vendors for those who were left homeless by the earthquake.

The conduct of these measures implied that the food shortage which occurred after the earthquake was not so much due to the lack of food but to its inability to reach the consumers. In fact, vegetables were rotting in Irisan, Baguio City just as fish were left untransported in the some coastal barangays of Agoo, La Union. Nonetheless, a widespread hunger was prevented by communities after the earthquake through measures which somehow managed to move food to where the demand was without using of the normal food routes.

Water Shortage and its Mitigating Measures. Another problem which prompted the communities to use its initiative was the water shortage felt in 46 communities or 96 percent of the total. The shortage came about when springs dried up, water pipes were busted, wells were contaminated, water supply systems halted operation and rivers, streams and irrigation canals were diverted. In 20 communities, nothing was done to mitigate the water shortage for two reasons. One was that the members managed it at the household level because either collective action failed to evolve or no need was seen for it. Another was that the water shortage was beyond the capability of the communities to handle such as the case of those in Pangasinan and La Union which went completely underwater.

Nonetheless, 26 communities or 57 percent of those undergoing water shortage mitigated the problem at the community level. In 13 communities, an inventory of the various water sources and their regular users was immediately done after the earthquake. The community leaders subsequently arranged with the users of those water sources which remained serviceable to share these with the users of water sources which were rendered useless by the earthquake. In one community, the use of private water tanks owned by its more affluent members was shared with the rest through rationing. In 9 communities where the earthquake impaired all regular water sources, new ones were developed by digging wells and improving access to existing springs. In 2 of these communities, pump wells which were disfunctional for years were repaired. The only recourse of 4 other communities in urban centers was to press their local fire department and other concerned agencies (such as the Local Water Utilities Authority) for periodic water delivery.

Electric Power Shortage and its Mitigating Measures. As it ceased the operation of power stations, toppled power posts and cut power lines, the earthquake deprived 46 communities, or 96 percent of the total, of electricity. In some communities, the absence of electric power took only three days whiles in others, it was as long as 60 days. The restoration of electric power took tinge particularly in 16 flooded communities. Among tire communities which were left without electricity, 31 communities fully left tire task of its restoration to the, concerned agencies. This wars the situation in communities where electricity returned shortly and in the ones which were largely depopulated by evacuation. Massive evacuation occurred in areas along the sea sand rivers where the earthquake brought about widespread flooding.

The outright result of the loss of electricity wars tire shortae of fuel for lighting and cooking. Sonic 10 communities coped with the shortage by using substitutes materials for fuel. Days after the earthquake, tire members of these communities camped in open spaces using firewoods for cooking and lighting. The firewoods were easily gathered in communities where there were standing woodlots. In communities where there were none, discarded lumber materials and old tires were collected from among the members. In tire evening, the bonfires made out of these materials lighted anal warmed their evacuation places. The restoration of electric power was hastened in 5 communities by work teams formed by their members. Working in coordination with the personnel of electric companies, these work teams reinstalled the power, post and removed the felled trees which cut the power lines. In one community where the electric company could not send a personnel, the restoration work was supervised by a community member who was an electrical engineer.

Demand for shelter its Mitigating Measures. The extensive damae of housing structures in 32 communities made shelter a serious concern. These communities comprised 67 percent of tire total. As the aftershocks kept on corning, more rnembers of these communities stayed out from the remaining standing houses and increased the demand for shelter. To meet the demand, various community-level measures were undertaken. Putting up common shelter was undertaken in 13 communities, These shelters were made of assorted materials gathered by the members in their own communities. Plastic sheets used as roofing of delivery trucks were made into tents and galvanized iron from damaged houses were made into leantos. Blankets, sacks and curtains were sewn together and palm leaves were woven into materials for temporary shelters. In one community, its leaders went from house to house to search for canvass tents. More materials were used by one community where monetary contribution wars solicited from among its members. Using such contribution, the community bought nails and timber.

To reduce the number of those in need of shelter, community-organized work teams repaired damaged houses in communities. The repair made many houses habitable although these may not be restored to their old forms. In 10 communities, the selection of evacuation sites were decided collectively. By publicly weighing the positive and negative features of each sites, the members' intimate knowledge of their own environment served as basis of the decision. While the process ensured the acceptability of the selected site, it also oriented the community members on the ways the resources and the constraints of the evacuation site can be managcd. In one community, the demand for shelter was relieved through an arrangement which enabled persons who were left homeless to stay with those whose houses were spared by the earthquake. Such arrangement was brokered by community leaders.

Road Closure/ Transport Shortage and Mitigating Measures. The earthquake caused the complete or partial isolation of 30 communities comprising 63 percent of the total. The transport lines which were lifelines to these communities were cut by landslides, ground ruptures and floods. Complete isolation meant that the land routes or waterways linking the community to the town or city centers became impassable while partial isolation meant part of it could not be reached from the community center. Because the communities relied on the town and city centers for a wide range of goods and services just as the population clusters within these communities relied on their centers, such isolation was easily translated into shortages. The need to restore the transport lines became more urgent as injuries and deaths occurred among community members.

To break the isolation, all the communities immediately organized work groups to clear the roads blocks. Using manual tools, these work groups removed felled trees and earth debris. Big boulders were removed in two communities through bulldozers and cranes borrowed from construction companies operating in their vicinity. Where there was no such equipment available, 5 communities gave up on road clearing and instead, opened alternative routes. This option involved the negotiation for a right-of-way and removal of obstructions such as fences and standing trees. In one community, P 10.00 was collected from every public transport vehicle who passed through the partially repaired roads to finance the remaining work required.

In three communities where the roads shortly became passable, isolation remained due to the absence of public transport. The public transport operators refused to ply in their usual routes because of the scarcity of gasoline. In response, a transport pool of private vehicles was created in two communities. The community members registered in advance their errands so that a trip to the city center carrying out all the errands could be planned. This reduced to a minimum the number of trips done by the community members. In one community where there were no private vehicles, an arrangement was made with a group of jeepney owners to provide one round trip to the city center once a day. The schedule of the trip was announced beforehand and the jeepney owners took turns in providing the vehicle.

Flooding and its Mitigating Measures. The flooding which occurred in 16 communities or 33 percent of the total was a result of various factors: liquefaction, diversion of waterways, obliteration of natural water gullies and the monsoon rains. Two or three of these factors worked in combination in all communities which were flooded. But flooding was intermittent and sectional in some communities while in others, it was continuous and extensive. In the latter communities, the water forced most members to evacuate. It was only after the water subsided that the evacuees resettled in these communities.

However, 10 communities undertook measures, 9 of which organized work teams who constructed canals to direct the flow of waters. The canals drained flood waters from evacuation sites and from routes to vital locations. These locations included water sources, health centers and gateways to city or town centers. Several days after the earthquake, the members of one community constructed an embankment to reduce the volume of water spilled from the river. The earthquake triggered the spillage and flooded the community.

Health and Sanitation Problems and Their Mitigating Measures. The health situation in 7 communities or 15 percent of the total deteriorated after the earthquake. This was indicated by the increased incidence of sickness especially among children. The exposure to the elements, the use of water from sources open to contamination, the deficiency of the available health care and the improper disposal of wastes contributed to such deterioration. Among these communities, 4 implemented measures aimed at improving the prevailing health situation. One made up the lack of modern medicine and medical personnel by using medicinal plants for treatment. Wounds and boils were cleansed with the broth of guava leaves and rheumatism was administered with coffee and eucalyptus leaves. These were administered by community members who were knowledgeable on the medicinal application of the plants in their immediate environment in spite of the advent of modern medicine. Such traditional knowledge came in handy when modern medicine was not available.

Another local resource which became very useful to one community was limestone mined from a nearby quarry. It reportedly retarded the decomposition of the bodies of the three community members who died and prevented the spread of foul odor. The community also shared the mineral with a number of communities which dead members could not avail of embalming services or immediate burial. In three communities, the sanitation in the evacuation sites was improved by having work groups construct temporary toilets. The toilets were made mostly of recycled materials such as gasoline drums for waste container. The toilets ensured that human waste did not find their way to water sources.

Sourcing and Sharing of External Resources

Although the households and communities affected by the earthquake used their own initiative and resources, external assistance was also needed. Such assistance was provided by other households within the community and by governmental and non-governmental agencies operating outside the community. The procurement of such assistance from these agencies and its distribution among community members generated some problems. Nonetheless, the manner these problems were handled stimulated creativity and showed the ways household and community initiative and resources could be complemented by external donors.

Assistance-seeking Among the Households. The self-reliance of households and commnities during the post-earthquake situation is indicated by the fact that 46 percent of the sample households did not seek assistance from outside their own household. Such assistance was sought by the remaining 54 percent. The percentage of assistance-seekers did not vary by status. They constituted 53 percent among the rich and 54 percent among the poor (Table 6). But to a certain extent, the propensity to ask assistance was determined by the impact the earthquake had on the physical assets of the households. Close to 58 percent of those with damaged houses sought outside assistance. Only 38 percent did the same among the households whose houses were spared by the earthquake.

The households who sought assistance tried to secure it from various sources. But the source that received most request was the non-governmental organizations, particularly the Philippine National Red Cross. Close to 73 percent of the assistance seekers asked assistance from these organizations. The community leaders followed the non-governmental organizations whose assistance was sought out by 42 percent of the households. Less households made their request to governmental organizations: 35 percent to national government agencies and 8 percent to city/municipal and provincial officials. Those who called upon their relatives constituted only 10 percent in spite of the existence of strong kinship ties. This may be due to the fact that 97 percent of the assistance seekers were looking for food. But because the earthquake cut-off almost all households from their food sources, no one had food to share.

Nonetheless, the relatives and the community leaders beat the non-governmental and governmental organizations in responding to the call for assistance. The response of their relatives came after two days and that of their community leaders came after three days. In contrast, it took an average of one week and 2 days for the non-governmental organizations to respond and one week and 5 days for the national government agencies. Despite the relatively slow response, 96 percent of the households received assistance. The assistance largely came in the form of relief goods. Among those whose houses were damaged, only 6 percent received assistance for repairs. Such assistance was either a loan from the Government Security and Insurance System (GSIS) or an aid from Department of Social Work and Development (DSWD). Among the affected farming households, none received any assistance for the rehabilitation of their farmlands.

Giving of AssistanceAmong the Sample Households. The households in an earthquakeravaged situation did not only display assistance-seeking behavior. Some 30 percent of them managed to help other households. However, the households who shared their own resources had certain characteristics. Assistance was dispensed by 38 percent of the rich households but only 25 percent of the poor households. Indeed, the leaders in 5 communities were reported to have received generous donation from among their wealthy members. There were also more who shared resources among households with undamaged houses at 47 percent. Among those with damaged houses, only 28 percent provided some form of assistance.

Both characteristics of most assistance-providers indicated that such behavior was partly a result of the existence of a surplus. Such assistance was provided by 43 percent to other members of their community and by 37 percent to their relatives. Only 20 percent gave to complete strangers. Food was the assistance provided by 62 percent. Another 38 percent shared their shelter and 11 percent gave money. The providers of clothes composed 5 percent and the providers of medicine, 3 percent.

Assistance-seeking Among the Communities. All the 48 communities studied received some form of external assistance after the earthquake. On the average, the assistance arrived three days since the earthquake (Table 7). The nearer the location of the community to the city or town center, the swifter the arrival of the assistance. Thus, Engineers' Hill which was adjacent to Baguio City center acquired said assistance four hours after the earthquake while Panganuan East in Aringay, La Union waited for four days. The waiting period was also stretched in communities which transport link with the city or town centers was cut by the earthquake. The communities received external assistance in two ways. One was through active procurement outside the community and another was through various entities who went to the communities to deliver such assistance. Active procurement occurred within two weeks after the earthquake. The delivery of relief assistance started four days after the earthquake and was still going on intermittently six months later.

There were 46 communities who actively search for external assistance after the earthquake. They went to the city and town centers to procure relief goods from the office of the mayor, the DSWD or some other governmental entities. In the process of procuring such assistance, 37 communities or 77 percent of the total encountered problems. All these problems were met at the source because these solely concerned the manner such assistance was given. The problem most frequently cited pertained to the lack of clear and definite location, procedures and requirements of relief procurement. This problem was cited by the leaders of 44 percent of the communities.

Most of the communities who had this problem were in Baguio City. This problem included the difficulty of locating the venue of relief distribution at a particular time and the confusion as to the step-by-step process needed for orderly and rapid dispersal of relief goods. At some points, certain documents (such as a household list) were reportedly made a prerequisite for acquisition of relief goods although the community leaders were not informed beforehand about such requirement. This further delayed the release of relief goods particularly to communities which were situated far from the center or which were rendered inaccessible to wheeled vehicles.

These uncertainties generated by the manner the relief goods was distributed to the communities were exacerbated by a host of other administrative problems. The leaders of 15 percent of the communities complained that while they were made to accomplish forms to obtain relief goods, the government personnel whose signatures were to be affixed in these forms were unavailable. In 9 percent of the communities, reports were made that their leaders competed with private individuals and non-governmental organizations in securing relief goods. In these communities, the leaders also reported that persons whom they did not know even procured relief by using their names. This situation occurred because there was no definite policy on who were authorized to obtain the goods from the distribution centers. Furthermore, no procedure was set on the proper identification of the legitimate representative of the community.

The leaders in 4 percent of the communities even made charges of discrimination in relief goods allocation. Such discrimination was purportedly based on kinship (relatives versus nonrelatives), ethnic strain (Lowlander versus Igorot) and political affiliation (Marcos versus Aquino follower). In one community, a leader said he was only able to speedily acquire relief goods for his constituency because a cousin manned the distribution center. The sum of these problems was the long wait in relief goods procurement as reported in 27 percent of the communities. Waiting for relief for as long as eight hours was reported in Baguio City.

Once the relief goods were released, transporting these from the town or city center to the community became a problem of 39 percent of the communities. The problem was easily handled by community leaders or members who owned vehicles. In communities where no vehicle was available, the community leaders rented one from the town or city center at usually very high rates. The rental was either paid out from the pocket of the community leaders or from the relief goods procured. The relief goods bound for communities which were not accessible by a wheeled vehicle or which roads were blocked by landslides or roadcuts were transported by work animals or by foot. This constraint delayed much more the arrival of the relief goods in the community. Upon arrival, the relief goods which were obtained at any one time were deemed in 9 percent of the communities as insufficient relative to the number of their households. Such insufficiency was reportedly borne out by the piecemeal manner the relief goods were released. .

However, a rationalization and streamlining of operation in distribution centers later mitigated many of these problems. In one town, the distribution of relief goods to the barangays was made in alphabetical order while in another, it was according to the barangay's distance from the town center. In both towns, the assistance was divided beforehand among the barangays to hasten their release. One of these towns also made it a policy to release the allocation of the barangay only to its captain to avoid duplication. One city scheduled the distribution of relief goods to minimize the waiting time spent by the community leaders. When the schedule was changed for some reason, a city employee was sent to the barangay captain to inform him ahead of time. A town and a city also divided their various barangays into areas of responsibility, each of which was assigned to a councilman to look after.

Sharing of External Assistance Within Communities. Food was the relief goods that reached all the communities. Only 55 percent of the communities secured medicine (including water purifier tablets) and 15 percent received plastic sheets which could be used as tents. Blankets were obtained by 8 percent of the communities and money, by 6 percent. For relief goods brought in by community leaders through active procurement outside, a distribution system was put in place. This system was managed mainly by community leaders in 62 per cent of the communities. However, in 19 percent of the communities, said leaders worked in tandem with.youth organizations (such as 4-H clubs and basketball associations). In another 19 percent, women organizations (such as Mothers Club and La Union Ladies Association) actively manned the distribution system. One community issued an identification tag to those who helped in distribution so that any misdemeanor could be easily reported to the leaders.

The distribution system was either based on the barangay or on its subdivision called the sitio. In barangays where the houses were largely clustered near each other, the barangay center served as the base of operation. Where the houses were scattered far apart as isolated farmsteads, the community leaders decentralized the operation by giving each sitio the power to manage each own distribution system. Under this situation, the external assistance procured by the community leaders was allocated to the leaders of each sitio, who in turn, allocated it to their constituent households.

These distribution systems haphazardly evolved in the communities. Many initially distributed the external assistance they received to individuals who formed a single file in front of the barangay hall or the captain's house. However, their leaders learned that this process favored the households with more members in the file and who were quick enough to run to the line whenever relief goods were available. The communities later implemented more rational assistance distribution systems some of which functioned better than others. These systems required in some communities the updating of their list of households to avoid duplication in distribution. One community opted to issue coupon to each household which must be presented and countersigned by the disbursing officer whenever its share of assistance was claimed.

There were two systems which were widely used: sectoral prioritization and equal distribution (Table 8). The sectoral prioritization distribution system was conceived and implemented in 54 percent of the communities. Under this system, external assistance was channeled directly to certain sectors of the community. The prioritized sectors varied among communities. In some communities, the evacuees obtained priority while in others, it was the indigents. In one community, the children and pregnant mothers were the prioritized sectors.

This system was well accepted in communities where the destruction of the earthquake was not widespread or where there was relatively wide gap between the rich and the poor. This was because those whose houses and livelihood sources-remained intact after the earthquake and those whose resource base was more than enough to replace the destroyed assets, did not look forward for such assistance: However, in five communities where most households were affected by the earthquake or which rich members were mere salaried employees, the system was considered as unjust. The core of the charge was the need for equal treatment among victims evacuees or non-evacuees, rich or poor, and displaced or non-displaced workers. The complainants maintained that every household was entitled to its share of any external assistance granted to the community regardless of their level of need. The rich in three communities rankled for a share of external assistance because their poorer relatives were in need.

Due to these complaints, some communities shifted to equal distribution system which
operated in 39 percent of the communities. This system worked in two arrangements. The
more widely used was the equal division among the households of any amount of external
assistance that reached the community. Under tires arrangement, the pre-packed bags containing anassortment of relief goods (such as rice, sardines milk and cooking oil) intended fear the consumption of care household was unpacked for distribution to all the households, household could hake home only a tin bean of rice or a tablespoon of cooking oil but no one had a bigger or smaller share than the other.

The other arrangement was adopted tea the fact that eternal assistance reached the community by batch and each itch was never enough for all the households. Thus, the leaders divided their community by segment and each was assigned as the beneficiary of a particular batch of assistance. Under this arrangement, the households received varying types of relief goods and bigger share, as compared to the ones under the first arrangement, rider both arrangements, goods, such as blankets and tents, which were too few to be divided among the households were given to certain sectors. For instance, nine community allocated the eight blankets it received to the elderly and mothers of new-born babies The 20 tents it received went try those who were left homeless try the earthquake.

By itself, the equal distribution of external assistance among households did not consider the varying level of need of the disaster victims. The system actually transferred to the household the power tea decide whether to share the assistance it received to the more needy. In five communities, a number of unaffected or rich households forewent their share in favor of the affected car the poor, But some of these; rich on unaffected households opted to get their share and gave it to their preferred beneficiaries,

Nonetheless, this system was criticized in four communities fear not taking into consideration the varying size of tire, households. Under both arrangements, the household with eight members obtained the same amount of assistance as the household eat only three members. One community made adjustment try using the number of pre-adolescent children in the household as basis in determining the amount of assistance that was allocated to it. Such action indicated that tire system underwent refinement as time went by to make it more suitable to the requirements of the community.

Two other systems were used lay a limited number of communities brat nevertheless served some purpose in their particular milieu. The house-to-house distribution system was used in only ease community. Such community had a small number of households who were living far apart front each other. Informing each household on the availability of external assistance took some tittle. Thus, the community leaders chose tea deliver the share of each to their respective house. The first-come-first served system operated in two communities. Except fear two dislocated water pipes, one was cart affected in anyway fry the earthquake, The other had affected households but they were generally affluent. Thus, the level of need for external assistance was low in both communities. To dispense the external assistance received by the community, its leaders simply give it away to any member who wanted some.

Issues in Distribution of Relief Assistance and Workable Strategies Regardless of the functioning of a distribution system used, there were issues which the community grappled with in managing external assistance. The issues which emerged in different communities indicated that the disaster situation in one community may be different from the rest. Nonetheless, not all communities confronting a particular issue were able to resolve it. But some communities were able to generate strategies which proved to be workable.

The first issue was how to guarantee the community leaders from suspicion of pilferage of external assistance obtained for the community. This issue arose in about half of the communities, most of which had relatively big population with factional groupings. But 10 communities formulated procedures to prevent such suspicion. These procedures required that upon arrival, the goods comprising the external assistance must be placed in a public building (schoolhouse, health unit or barangay hall) and must be distributed to the households before nightfall. Thus, the community leaders must alert beforehand the potential beneficiaries of the arrival of the external assistance.

The second issue was whether the external assistance obtained by the community should be shared with non-community members who were stranded or temporarily taking refuge. Five communities sheltered outsiders for about a week after the earthquake. These outsider were either students, mine workers and passer-bys who were trapped in the community by road closures or were evacuees from other communities. For those who were merely stranded, one community negotiated with its more affluent members to temporarily accommodate them until transportation was available. Some of these refugees were even provided transport fee by their hosts. However, the case of the evacuees was more controversial be cause sharing with them the community's resources ignited resentment from the members One community resolved the issue by obtaining the services of the DSWD to take care o1 the evacuees who were taking refuge in its schoolhouse.

The third issue was what to do with an external assistance which did not respond to the needs of the community. One community received seeds of crops which were not suitable to the type of its soil. The seeds which may be useful to another community was simply wasted. Two communities received food assistance which they did not need. Because the earthquake occurred after the harvest season, one rice- growing community with enough rice-stock received rice from outside sources. The rice donation which were distributed to the members promptly found their way to the market. The other community was initially it need of food but the foodstuff kept on coming within six months after the earthquake. As a result, a number of community members halted the cultivation of their plots and learned to depend on the dole-outs. The dependence that the external-assistance developed, by itself became a community problem.

The fourth issue was whether governmental and non-governmental organizations be allowed to directly distribute assistance to the households and bypass the existing community distribution system. Thirty-nine communities who were visited by these organizations allowed them to provide direct assistance and some even provided them with list of households. However, these organizations managed only to reach a portion of the community members, many of whom were living along the roadside. Because of the uneven benefit that these visits provide, resentment developed between the beneficiaries and non-beneficiaries and between the community members and their leaders. One community, charged its leaders of putting only selected names in the list of households provided to these organizations. Another community had households who managed to wring so much goods from external donors that they were able to sell some of these to their neighbors. In three communities, the non-beneficiaries sought to off-set their loss by obtaining more from the existing distribution system. But being dependent on external sources, the system could not match the assistance provided by the more resource-rich governmental and non-governmental organizations.

Uneven direct provision of assistance from outside may also build dangerous expectations among the non-beneficiaries. The case in point is the housing assistance provided by the government. Totally destroyed houses were found in 24 communities. But six months after the earthquake, there were only 3 communities where all the owners of the damaged house got housing assistance. No one obtained assistance in 6 communities. In 15 communities, assistance was given to some but not to all owners of damaged houses. For example, only 6 out of 12 obtained housing assistance in Pinget, Baguio City and 19 out of 49 in Santa Barbara, Agoo in La Union. Those who did not get the housing assistance nagged their community leaders. Some secured debt for house construction with the expectation that it can be repaid by the government housing assistance. Six months after the earthquake, such assistance did not yet come. This left the houseowner with a debt the interest of which grew day by day. Thus, the direct administration of external assistance can shred not only the cohesion of the community bound together by a common effort to survive but also the wellbeing of an individual.

 

SOME CONCLUDING NOTES

The study established that the households in the study sites were unaware that they were living in a geologically risky area and were unprepared for the July 1990 earthquake. Nonetheless, they responded to its impact through collective effort and by making use of available resources within their environment. Through such effort, road blocks were cleared, houses were repaired, services were restored and lives were saved. The resources in their environment readily substituted the conveniences of modern living --- herbs instead of manufactured medicine, spring water instead of tap water, bonfires instead of electric lights and lime deposit instead of chemical preservatives for the dead. The communities who managed to have these resources were less dependent on external assistance. Their collective effort and creative- use of available resources ensured their survival and the restoration of their former lifeways in spite of the failure of the governmental and non-governmental organizations to provide an immediate response.

Notwithstanding, most households and communities sought external assistance. The procurement of such assistance was encumbered by the administrative shortcomings in distribution centers and lack of transportation. But once the goods comprising the assistance reached the community, these were distributed according to some systems which the community evolved through trial and error. The distribution systems varied among communities but generally worked to uphold their members' concept of fairness. However, some governmental and non-governmental organizations later directly distributed their assistance to some community members. By bypassing the community distribution system, a number of undesirable consequences resulted. The most grave was the weakening of the cohesion of the community which should hold together more steadfastly at such a time.

The experience of the households and communities of Northern Luzon indicated that they have the capability to manage a disaster situation. This capability was exercised in a haphazard manner mainly because of their unpreparedness for the disaster. It, nonetheless, produced workable strategies for disaster mitigation which were tailored to needs of the community. These strategies can serve as basis for a disaster mitigation program with the community as the centerpiece. The program can strengthen both the organizational and environmental capability of the community. It will also ensure that the effort of governmental and non-governmental organizations should merely supplement but not supplant that of the community. In this manner, the capability of the community to rely on itself will propel it not only to survive in a disaster situation but also move forward in normal times.

 

SOME CONCLUDING NOTES

The study established that the households in the study sites were unaware that they were living in a geologically risky area and were unprepared for the July 1990 earthquake. Nonetheless, they responded to its impact through collective effort and by making use of available resources within their environment. Through such effort, road blocks were cleared, houses were repaired, services were restored and lives were saved. The resources in their environment readily substituted the conveniences of modern living --- herbs instead of manufactured medicine, spring water instead of tap water, bonfires instead of electric lights and lime deposit instead of chemical preservatives for the dead. The communities who managed to have these resources were less dependent on external assistance. Their collective effort and creative- use of available resources ensured their survival and the restoration of their former lifeways in spite of the failure of the governmental and non-governmental organizations to provide an immediate response.

Notwithstanding, most households and communities sought external assistance. The procurement of such assistance was encumbered by the administrative shortcomings in distribution centers and lack of transportation. But once the goods comprising the assistance reached the community, these were distributed according to some systems which the community evolved through trial and error. The distribution systems varied among communities but generally worked to uphold their members' concept of fairness. However, some governmental and non-governmental organizations later directly distributed their assistance to some community members. By bypassing the community distribution system, a number of undesirable consequences resulted. The most grave was the weakening of the cohesion of the community which should hold together more steadfastly at such a time.

The experience of the households and communities of Northern Luzon indicated that they have the capability to manage a disaster situation. This capability was exercised in a haphazard manner mainly because of their unpreparedness for the disaster. It, nonetheless, produced workable strategies for disaster mitigation which were tailored to needs of the community. These strategies can serve as basis for a disaster mitigation program with the community as the centerpiece. The program can strengthen both the organizational and environmental capability of the community. It will also ensure that the effort of governmental and non-governmental organizations should merely supplement but not supplant that of the community. In this manner, the capability of the community to rely on itself will propel it not only to survive in a disaster situation but also move forward in normal times.

 

REFERENCES

Caroll, John J. and Salvador A. Parco. 1966. Social Organization in a Crisis Situation: The Taal Disaster. Manila: Philippine Sociological Society.

National Statistics Office. 1990. Statistical Handbook of the Philippines. Manila.

Office of the United Nations Disaster Relief Coordinator. Disaster Prevention and Mitigation: A Compendium of Current Knowledge. Social and Sociological Aspects. Vol. 12. Geneva.

Philippine Institute of Volcanology and Seismology. 1985. Environmental Impact Study of the 1984 Mayon Volcano Eruption. Unpublished Report. Quezon City.

Jean C. Tayag and Sheila I. Insauriga
Philippine Institute of Volcanology and Seismology

 

ABSTRACT

The response of government and non-government organizations to the July 1990 Luzon earthquake disaster was assessed from three viewpoints--those of the media, government disaster management officials both at national and local levels, and the affected inhabitants. Press coverage of the earthquake disaster clearing the three weeks after the earthquake was reviewed; key informant interviews were conducted among national and local disaster management officials and NGO leaders; and a household survey was undertaken to gather the affected inhabitants' views.

The three viewpoints agreed can at least two points: that the government (both national and local) response left much to be desired: and that non-government and private organizations exhibited great initiative and played an active role during the disaster. Both media and the national disaster management officials assessed that the local bodies in charge of dealing with disasters-the Disaster Coordinating Councils (DCCs)-were incapable of promptly responding to the situation. Acting on this assessment, the President created Disaster Relief Coordinating Teams to coordinate rescue and relief activities the hardest hit areas. These teams were headed by Cabinet officials and superimposed can the local DCCs. Implicitly assuming a similar assessment of the local DCCs (in)capability, numerous NGOs rushed to the disaster areas and directly distributed relief goods/assistance to the victims without coordinating with the concerned government units, adding to the confusion and resulting in duplication of efforts, disproportionate distribution of relief and other problems.

Local disaster management officials interviewed acknowledged their lack of preparedness plans, resources and authority to deal with a major earthquake. However, the local organizations were not totally incapacitated. After recovering from the initial shock, they moved, though not always as DCCs but as individual DCC member organizations. A majority of the local DCCs were able to mobilize 34 days after the event. Several DCCs did not meet but their leaders and some of their member organizations were in the front tine. The respondents among the affected inhabitants likewise recognized the role played by government units, specifically the Department of Social Welfare and Development and barangay leaders although the DCC was not a known entity to them.

Organizational experiences in the 1990 disaster underscored several issues which need to be resolved to prepare the country for similar occurrences in the feature: 1) the most appropriate and effective organizational framework for disaster response; 2) division of disaster management responsibilities among: the various levels of organization -- national, regional, provincial, municipal, barangay, and household; and 3) the role of NGOs in disaster management.

 

INTRODUCTION

The strongest and most destructive earthquake to hit the Philippines in the last two decades struck on 16 July ,1990 with a magnitude of 7.8 on the Richter scale and a maximum felt intensity of VIII in the Modified Rossi-Forel (MRF) scale (VIII- IX in the Modified Mercalli scale). The epicenter of the event was located at near the town of Rizal? Nueva Ecija, at a depth of 28 km. This major earthquake and its attendant geologic processes--surface faulting, liquefaction, landslides and debris flows-- exacted a toll of 1283 dead, 2786 injured, 321 missing (NDCC, Nov. 14, 1990) and more than P18.7 Billion in actual damages to public infrastructure and facilities and private properties (NEDA, Nov. 1990). Four regions in north and central Luzon suffered the heavy damage and casualties with the cities of Baguio, Dagupan, Cabanatuan and San Jose bearing the brunt of the disaster.

In the first days and weeks after the disastrous event, governmental and non-governmental organizations or institutions were hard-pressed in undertaking tasks brought about by the disaster-the rescue and recovery of trapped or isolated victims; the provision of food, clothing, medical attention, and temporary shelter to the displaced; and repair and restoration of function of power, water and other utility systems, transportation and communication.

A report of the United Nations Disaster Relief Office (UNDR0, 1986) pointed out a number of myths about or popular images of organizational response in emergencies which have been found to be often incorrect, leading to negative consequences or administrative difficulties in meeiing disaster needs and managing relief and recovery operations. Among the popular assumptions is the myth of overwhelming impact on local leadership- according to which local organizations in a disaster area are overwhelmed, rendered ineffective, lacking both leadership and personnel. Logical moves based on these assumptions are: 1) the imposition of strong centralized leadership by some unaffected outside person to cope with the confusion; and 2) direct distribution of relief and assistance from donors to recipients, resulting in inappropriate relief, superfluous volunteers and duplication of efforts.

How applicable were these popular images of organizational response in the areas hit by the 1990 earthquake? Were the local organizations overwhelmed and incapacitated? How did the local disaster concerned organizations particularly the DCCs measure up to the tasks of coping with the disaster? How did the national government and private and nongovernmental organizations (NGOs) respond?

The aim of the study was to assess the response of organizations and institutions to the July 1990 earthquake disaster in Luzon, from at least three viewpoints-- those of the media, the government disaster management officials and the affected inhabitants. It was hoped that in the process, the lessons imparted by the experience could be underscored and alternative solutions explored.

 

PROCEDURE

To gather data on media assessments, articles, columns and editorials on the earthquake in eight major dailies during the two weeks after the event were reviewed. For the government's self assessment, available reports of government disaster management oganizations were content analyzed and key informant interviews ere conductd among national sand local disaster management officials and NGO leaders. To get the views cat the affected inhabitants, the survey instrument. of the household d community survey part of the project was made it) carry several questions relevant to organizational response. Data gathering and summing up of assessments were focused mainly can the rescue and relief aspects of disaster management activity.

FINDINGS

Media Assessments

The media, broadcast and print, played a very active role during the disaster period. Mediamen were in the frontlines, documenting and reporting rescue-relief operations, attending to the information needs of affected inhabitants as well gas disaster management units, pointing cut areas that needed attention, generating sympathy and assistance for the victims and providing alternative communication links when public facilities broke down. It was therefore understandable that the reports of media people influenced subsequent responses of disaster management organizations.

Most of the columns reviewed pictured the disaster as widespread and described the rescue and relief efforts as disorganized, uncoordinated, slow, inadequate, unprepared, and ill equipped. These also claim that it was the non-government sector which took the lead in performing functions which should have been performed by the government. The unsatisfactory performance of disaster response agencies was blamed on the government's lack of disaster preparedness, lack of planning, weak leadership, inadequate attention and funding support for disaster management, lack of rescue equipment and properly trained rescue manpower, lack of transportation and communication facilities, bureaucratic red tape, and a host of other factors. The extensive damage was likewise attributed either to inadequacies in the Building Code or in its enforcement.

See Appendix 1 for illustrative excerpts,

 

National Government Response and Self-Assessment

During her visit to the disaster areas, the president of the country observed a need for leadership and organization in the rescue and relief efforts and was quoted to have exclaimed: "Who's in charge here?". To fill in this need, President Aquino created by Administrative Orders Disaster Relief Coordinating Teams (DRTC) for Baguio City (AO 183); for Pangasinan (AO 184); Nueva Ecija-Nueva Vizcaya (AO 185); and La Union (AO 189). These teams were tasked to take charge of and coordinate all rescue, recovery and relief operations of government and non-government organizations in their assigned areas with the, Disaster Coordinating Councils (DCCs) of the regions, provinces, and municipalities or cities under them.

The Baguio Disaster Relief Coordinating Team was headed by the then Executive Sec. Jose do Jesus, the Pangasinan team by Sec. Bengzon of the Department of Health, the Nueva Ecija - Nueva Vizcaya team by Engr. Manuel Estrella of Philippine National Oil Company (PNOC); and the La Union team by DPWH Edmundo V. Mir.

In addition, an Earthquake Assistance Center was set up at the Office of the President. Headed by Elfren Cruz and staffed by the Presidential Management Staff, the Center was to serve as link between Malacanang and all other government agencies involved in rescue and relief operations and to coordinate all foreign assistance,

The President declared state of calamity in the hard hit areas and issued executive and administrative orders to facilitate and govern disaster response activities. Among these Presidential actions were: authorization of importation and donation of relief and rehabilitation supplies to the victims of the July 16, 1990 earthquake; price control can prime and essential commodities; authorization of the advance payment of one half of the Christmas bonus and the additional cash gift to all government officials and employees residing in assigned or calamity areas; review and update of the Medium Term Philippine Development Plan for 1990 to include therein the reconstruction and development program for the regions, provinces, cities and municipalities affected by the earthquake; and creation of a Presidential Task Force for the Rehabilitation of the Areas Affected by the July 16 Earthquake.

In a report to President Aquino, NDCC Chairman Fidel Ramos (NDCC, Aug.2l, 1990) stated that on the whole, the government's response to the disaster under the coordinated umbrella of the NDCC "has been satisfactory, although certain significant deficiencies were observed" which, he promised the Council will strive to rectify toward a more effective and well coordinated disaster management.

The most visible involvement of NDCC member agencies were in rescue, transport and provision of relief and medical assistance, restoration of public utilities and services.

Although the NDCC cannot claim credit for leading and undertaking rescue and recovery operations in Baguio City, the military arms of the government and which could also be considered arms of the DCCs were actively involved in rescue and recovery work in Benguet, Dagupan, Nueva Vizcaya, Cabanatuan and other parts of Nueva Ecija, although their work was hampered by lack of equipment.

The national DCC was also responsible for bringing into Baguio City medical teams of the Department of Health to assist the provincial hospital staff in attending to the victims.

While Baguio was cut off, relief was airlifted from a staging point at San Fernando La Union via a relay of helicopters provided by Philippine Air Force. Relief goods to the municipalities of Benguet were also ferried by helicopters as the Baguio-Bontoc Road was impassable.

For Nueva Vizcaya, relief goods were airlifted from Manila to Kawayan, then transported by trucks to Bagabag-Aritao where a staging center was established, manned by elements of the Philippine Army 5th Division. From here, relief goods and rescue medical teams were brought by air to the affected areas. Some of the relief goods from Cagayan were transported by land direct to Aritao.

In Dagupan City, the immediate need was water. This was partly alleviated in the beginning with 10 fire trucks from the PC/INP.

Clearing and repair were also immediately started on San Jose- Sta. Fe Road in Nueva Ecija by DPWH and AFP engineers working on both ends. On 13 August, this road was opened with load limitations which the local PC was tasked to enforce.

The Department of Public Works and Highways (DPWH), a member of the DCC, and military engineering brigades were responsible in road clearing operations and restoration of public utilities and services, especially in Baguio City. Patch up work was done on the runway of Loakan airport so that it was opened to limited traffic on 18 July, 2 days after the quake, enabling PAF planes to bring in relief goods to the city on the same day. Damaged sections of the Naguilian Road were rush-repaired by DPWH work teams assisted by AFP engineers and on 20 July, the road was partially opened and access to the city was restored.

Electric power was initially restored in some portions of the city on 18 July up to 26 July. By 2 August, power was completely restored. Water supply was completely disrupted. At the start, water was provided by 20 fire trucks brought by the PC/INP which came through on 21 July when Naguilian Road was opened. By 26 July, 14 out of the 35 pumping stations were operationalized partially restoring the city's water supply system.

Telephone communication within the city and with the outside was restored on 2 August.

In a meeting, NDCC officials (Minutes, August 10,1990) pointed out that Disaster Coordinating Councils (DCCs) had already been created all over the country and that 95% should have been operational when the earthquake struck. Moreover, the National Calamities and Disaster Preparedness Plan provides policy guidelines and SOPs in calamities/disaster operations. The NDCC issued in 1989 Memorandum Orders to lower DCC Chairmen to provide for community-based rescue, evacuation and relief operations during disasters; consolidation of all reports to prioritize release of funds; establish procedures for recommending the declaration of a state of calamity; policies and procedures in requesting, allocating, releasing and monitoring of calamity funds; and policies and procedures on foreign assistance. The national disaster management officials stressed that these policies point to the local DCCs at the regional, provincial, city/municipal and barangay levels as the backbone of the national disaster rescue-relief organization. The effectiveness and efficiency of the entire system therefore depends on these local subsystems.

NDCC officials also stressed that there are sufficient plans some of which have even been further detailed and operationalized by local DCCs. Despite the existing policy guidelines and plans, the July (earthquake disaster brought to light the following deficiencies (NDCC, Aug. 21, 1990):

1. Failure of some local DDCs to react and take charge. Some local officials were caught unaware, resulting in the failure to take charge.
2. Lack of coordination between and among NDCC member agencies/NGOs especially in the allocation and distribution of relief goods resulting in the slow or non-delivery of assistance in affected areas. The NGO relief agencies did not seek the advise of the government regarding the relief requirements in the affected areas. They started to distribute their relief good on their own which sometimes resulted in the disproportionate distribution of relief goods.
3. Need for the establishment of effective management of relief centers and staging areas for relief goods in the matter of cargo storage, handling and packaging, etc., to insure timely relief responses in affected areas.
4. Need for an effective quick response rescue/recovery capability. The rescue volunteers/teams who responded have very little capability except raw manpower.
5. Need for the pre-inventory of rescue capability of private firms and harnessing them for rescue/relief operations. The disaster revealed the inability of some DCCs to immediately provide local rescue equipment/tools to responding teams despite their availability in the community.
6. Need to decentralize decision-making on rescue, recovery and relief management to task agencies so as to hasten the delivery of emergency services in the affected areas.
7. Need for back-up communications systems between affected areas and the RDCC and NDCC. Most often, during disasters of large magnitude, communications lines are cut off due to power failure which therefore necessitates back up communication systems powered by batteries or emergency generators.
8. Need for immediate damage assessment information as basis of decision making by NDCC and tasked agencies.
9. Lack of accurate knowledge of alternative routes to isolated areas, which prevented relief agencies of the government of the government and the NGOsfrom proceeding to the affected areas.
10. Need to coordinate and facilittate entry of foreign assistance. The delays caused by this shortcoming may have caused the loss of some lives.
11. Low level of public awareness and preparedness of Filipinos about geologic phenomena like earthquakes, volcanic activities, landslides, etc.
12. Lack of measures to prevent probable cascades of disasters. The typhoon which followed the earthquake produced additional hazards that may have been avoided if our forests had not been denuded.
13. Need for proper and effective land use management and inclusion of preventive measures against adverse effects of geologic hazards in urban developments;
14. Need to upgrade earthquake monitoring in the country.
15. Need for update and implement the Building Code of the Philippines.

Local Government Accounts

Interviews with local government officials and NGO leaders yielded the following eyewitness accounts and self assessments on local government units' response to the disaster particularly that of the local DCCs.

In Baguio-Benguet

The first organized rescue response was that of the cadets of the Philippine Military Academy, a government institution, though not a member of the local DCC. By midnight of July 16, the cadets with some miners were pulling out survivors and casualties from the collapsed buildings in Baguio.

On day 2, July 17 in the afternoon, CRECOM Commander Brig. Gen. Juanito Aquias tried to convene the Regional Disaster Coordinating Council (RDCC) but could not gather enough members to launch a full scale disaster response. Volunteers crowded at the Baguio Fire Station, the RDCC center.

On day 3, July 18, the surrounding mining communities such as PHILEX, Antamok, Lepanto and various mines under Benguet Corporation responded to the RDCC's distress call for rescue. Armed with jack hammers, stone chisels, hacksaws, acetylene torches, spades and shovels, the miners worked round the clock. Their large lifting jacks were mostly ineffective inside the rubble. Their efforts were further hampered by heavy rains and continuous aftershocks.

Volunteer doctors arrived from Manila via San Fernando airport.

On July 19, the initial batch of Japanese rescue and medical teams arrived.

On July 20, the first Regional Disaster Coordinating Council meeting was held. This was held jointly with the Sangguniang Panlalawigan. In the meeting, the RDCC made important decisions/policies that were to govern the Council's and the member agencies' actions during the crisis (Minutes, July 20,1990).

On reporting, it made it SOP for barangay officials to report to Mayors who would in turn consolidate and submit reports of damage and casualties to the Provincial DCC. Said reports were to be the basis for assistance.

On relief, it designated the Department of Social Welfare and Development(DSWD) Provincial Office as the lead agency with Philippine National Red Cross (PNRC)-Benguet Chapter, and other government agencies and volunteer groups in supportive role.

Initial assistance to province like food and medicines were to be divided equally based on assumption that all 13 municipalities were affected. Later, distribution would depend on need.

Assistance to municipalities would be coursed through Municipal DCCs headed by mayors which will be responsible for distribution.

On rehabilitation, priority were the opening of roads in the following order: Naguilian, Halsema, Kennon and Benguet-Nueva Vizcaya roads. The lead agency would be the DPWH with assistance of other government agencies and private firms.

On funding, the Sangguniang Panlalawigan appropriated P900000 for mobility, repair/maintenance and food and medicines.

On other matters, the Vice Governor would coordinate road opening activities while the Executive assistants would coordinate airlifting activities; All stranded Benguet students were to be accommodated at Benguet State University gymnasium; Medicine distribution was placed under the coordination of Asst. Provincial Health Officer while use would be coordinated by Municipal Health Officers.

On the same day; the NGOs met to consolidate relief efforts at a local radio station. At the request of a Cabinet secretary, the NGO representatives to the RDCC formed themselves into the adhoc Regional NGO Coordinating Council (RNCC)

It therefore took 3-4 days to set the regional disaster response machinery into more orderly action. Meanwhile, the first 3 days were admittedly characterized by confusion and lack of direction and coordination, with volunteers, relief goods, communication equipment, vehicles, government personnel massing at the RDCC center waiting to be mobilized.

In Dagupan City

The officials interviewed acknowledged criticisms regarding the slow response of the city government.

Regarding the preparedness of the CDCC, it was admitted by the respondents that the Council had inadequate capability to cope with such a large scale calamity. The council normally meets during May and June, before the typhoon season and is prepared only to deal with typhoons and floods. Its preparedness plan is also appropriate only for these types of calamities.

Moreover, the earthquake was not localized. It had widespread impact. The CDCC had inadequate manpower, skills, equipment and authority to cope with the disaster. It did not have the authority to order DPWH to give its resources to help Dagupan.

Nevertheless, the CDCC responded belatedly by organizing local leaders, pinpointing immediate needs, and mobilizing government officials, business and other non-government groups to restore power, telephone systems, water supply and other utility systems. The most visible national organization which helped in rescue operations was the Philippine Navy
Task Force Tulong. Relief was largely provided by NGOs and private groups/individuals. Most of the NGOs from Manila directly distributed to recipients or coursed relief through local NGOs.

In Cabanatuan

Like Dagupan, the Cabanatuan DCC had no plans for earthquake disaster response, only for typhoons. It usually meets only when typhoon signal number 1 is raised.

There was no time for the DCC to meet but response was spontaneous. First to respond were the Mayor, PC Commander, Fire Chief, Police Chief, barangay captains and the DSWD.

To rescue those trapped in the collapsed Philippine Christian College, the first to arrive, on the scene can July 16 were some 395 soldiers of the 7th division in Fort Magsaysay under Brig. Gen. Calupig. In the morning of July 17, elements from the US Air Force and Navy Seabees numbering 201 arrived from Subic escorted by Mayor Gordon of Olongapo City. These two units combined rescue efforts. A company of the AFP Engineers also came later. The Americans brought in a telescopic crane, augmented by a similar equipment from the local DPWH. A British rescue team of 16 also arrived on July I'7. In days round the clock operation, a total of 278 were rescued, 137 of whom were injured and 141 dead were recovered. Rescue operations were terminated on July 26. As in Baguio, the local rescue teams load inadequate equipment.

Two centers of action were set up--Bahay Tulungan for donations and Liwag Building for rescue. Many private individuals and NGOs assisted. Most of the NGOs, however, did not pass through the DCC or DSWD but distributed their relief goods directly to the victims. Unlike in the Baguio, the NGOs in Cabanatuan did not form an umbrella NGO organization. Their networking was described as adequate, though.

Assessment of Household Respondents 

The interview schedule for the household and community survey included some questions which were intended to gather the respondents' views on the performance of organizations during the disaster.

Two questions on the seeking and receipt of assistance: showed that of those who sought assistance from outside the household (54% of the total number of respondents), about 73% sought the help of NGOs, particularly the Philippine National RedCross (PNRC). Next most sought out sources of assistance were community or barangay leaders and government agencies particularly the DSWD (both approached by 42% of the respondents). Only 10% sought the assistance of relatives and 8% went to their municipal/city or provincial officials. Most of the respondents seeking assistance were after food, one of their most pressing problems.

Average response time of the approached organizations ranged from 2 days to 12 days. Assistance from national government agencies and NGOs took longest to reach the assistance seekers (12 days and 9 days, respectively). In contrast, response of or assistance from relatives and barangay leaders took only 2-3 days (Table 1).

Most of the households received relief goods. Among those who had damaged houses only 6 % received assistance for repairs, in the form of either a loan from the Government Security and Insurance System (GSIS) or of an aid from DSWD.

The respondents were also asked to identify the organizations/persons they perceived as most active during the various phases of the disaster.

During the rescue phase, military units like the PMA (in Baguio- Benguet) and the Philippine Navy (Dagupan-Pangasinan) were the most visible, followed by NGOs and private establishments and individuals, then by foreign rescue teams (Table 2).

For the relief aspect, on the whole, the NGOs were the most frequently mentioned. The most appreciated NGO is the PNRC, followed by others like the Montanosa Relief and Rehabilitation Services (MRRS) and ABS-CBN Foundation; International Lions Club, Jaycees, DWZN, Rotary Clubs, professional organizations and religious groups. In Dagupan however, the most frequently mentioned were the barangay leaders, followed by NGOs. In Dagupan, NGOs were the most ubiquitous, followed by DSWD.

In rehabilitation, the respondents merely mentioned the "Government" without distinguishing which unit or level.

CONCLUDING OBSERVATIONS

The three viewpoints agreed on at least two points: that the government (both national and local) response left much to be desired; and that non-government and private organizations exhibited great initiative and played an active role daring the disaster. Both media and the national disaster management officials assessed that the local bodies in charge of dealing with disasters - the Disaster Coordinating Councils (DCCs) were incapable of promptly responding to the situtation. Acting on this assessment, the President created Disaster Relief Coordinating teams to coordinate rescue and relief activities in the hardest hit areas. These teams were headed by Cabinet officials and superimposed on the local DCCs. Implicitly assuming a similar assessment of the local DCCs (in) capability, many NGOs converged in the disaster areas and directly distributed relief goods/assistance to the victims without coordinating with the concerned government units, adding to the confusion and resulting in duplication of efforts, unbalanced distribution of relief and other administrative problems.

The criticism of the media and disaster management officials at the national level that the local DCCs had no preparedness plans and resources to deal with a major event like the July 16 earthquake was acknowledge by the local and national disaster management officials. The local DCCs could hardly have been expected to possess the equipment needed for rescue and recovery such as telescopic cranes and sensors. But to say that the local organizations were totally incapacitated would not be accurate either. After recovering from the initial shock, they moved, not as DCCs but still as local organizations or units. The experience of Cabanatuan illustrates this. Even if the DCC did not meet, the DCC leaders and some DCC member organizations were in the front lines. The respondents among the affected inhabitants likewise recognized the role played by government units, specifically the DCC and barangay leaders although the DCC was not a known entity to them.

Organizational experiences in the 1990 disaster underscored several issues which need to be resolved to prepare the country for similar occurrences in the future: 1) the most appropriate and effective organizational framework for disaster response; ) division of disaster management responsibilities among the various levels of organization -- national, regional, provincial, municipal, barangay and household; and 3) the role of NGOs in disaster management.

On the most appropriate and effective organizational framework for disaster management

The effectiveness of the NDCC itself has been questioned--its nature as a mere coordinating body, constituted by department heads (who usually come and go with the President), headed by the Department of National Defense (DND) Secretary ; its lack of permanent and independent staff and its dependence on the lead agency-DND for secretariat work and operating resources. The local DCCs are equally or even more unstable. Each is headed by the chief local executive-governor for province and mayor for city or municipality--with the organic local officials, national officials working at the local level, together with civic, religious and professional organizations as members. The elective political leader and the officials appointed by him are with the DCC only during their elective term; the line agency officials operating in the local area are under the authority of and follow the priorities set by their respective mother departments. The setup is known to be plagued by coordination problems.

The so-called failure of the DCCs to promptly provide the leadership and machinery to harness the groundswell of volunteerism and organize the rescue and relief operations led the President to create disaster relief coordinating teams for Baguio City, Pangasinan, La Union and Nueva EcijaNueva Vizcaya Cabinet men were appointed to head the first three and the President of the Philippine National Oil Co. to take charge of the fourth. These teams were super-imposed on the local DCCs ( Fig.l). In addition, an Earthquake Assistance Center was set up at the Office of the President, headed by Secretary Elfren Cruz of the Presidential Management Staff.

Were these necessary, really and for how long? How viable an alternative is the Disaster Relief Coordinating Team set up? Could it take the place of the NDCC or higher level DCC? This question remains to be resolved. It might however, be worth pointing out that before the end of July, Sec. De Jesus of the Disaster Relief Coordinating Team for Baguio decided to decentralize relief operations in Baguio City due to criticisms that help had been slow in coming to the victims. The move was also prompted by the reported incidence of pilferage and misuse of relief goods. The decentralized system would use the existing city government structure-with a committee headed by the mayor and representatives from DSWD and NGOs as members--in other words-- the local Disaster Coordinating Councils with another name--Disaster Coordinating Committees. The DSWD would determine the allocation of relief goods to each barangay which would have its own disaster coordinating center. NGOs which had been conducting their own relief work, would also coordinate with the city committee to avoid duplication of function.

For Benguet, a Disaster Coordinating Committee was also organized with the Governor as Chairman. Relief goods would be distributed through the mayors of the 13 towns in the province. The DRCT for Benguet was thus phased out on July 30 and the local government took over the residual activity of rescue and relief.

The need for a more effective disaster management organization was also pointed out by the UNCHS (Dec. 1990) whose recommended alternative is either an improved NDCC or a new organization.

Five bills were introduced at the House of Representatives, seeking to create another organization for disaster control and management. One recommends an independent, permanent administration-type organization; three propose an authority type body to be directly placed under the Office of the president; and another one proposes a council like NDCC but with expanded functions (House Bill Nos, 22363, 31521, 31570, 32997, 31700).

At least three characteristics of the DCC set up have been blamed for its shortcomings and used as rationale for considering alternative organizational frameworks: its being a coordinating body, its ad hocness and limited disaster management thrust focused on response. But--would a specialized, permanent and all- encompassing disaster management body be more effective?

A disaster, by definition, affects all aspects of a community's life. Dealing with it therefore calls for the involvement of most if not all of the affected polity's institutions/organizations. A coordinating body, headed by the most authoritative leader of the affected area, is therefore the most logical organization for dealing with disasters.

The DRCTs superimposed by the Cory Administration on the local DCCs were even more adhoc than the DCCs while the Disaster Coordinating Committees were actually Disaster Coordinating Councils with another name. The Presidential Task Force for Rehabilitation of Areas Affected by the July 16, 1990 Earthquake was likewise more ad hoc than the DCC.

The adhoc versus permanent issue cannot be divorced from the limited versus allencompassing question. What aspects of disaster management are to be handled by the desired organization?

Disaster management encompasses a wide range of disaster-related activities that are undertaken before, during and after the occurrence of a disaster-causing event, namely: hazards assessment and zoning, disaster protection and risk reduction, monitoring and prediction, contingency planning, emergency response, recovery, rehabilitation and reconstruction or redevelopment. A single all-encompassing disaster management organization to handle all these aspects would practically be a superbody.

There are already existing organizations handling each of these aspects, albeit separately. Hazards assessment and zoning are done by technical agencies like PHIVOLCS (for geotectonic phenomena) and PAGASA (for atmospheric phenomena); Risk reduction in the form of land use planning and control, and adoption of appropriate disaster-resilient building design and construction are the responsibility of the NEDA and the DPWH in cooperation with local government units; the installation of disaster protection structures like sabos and dikes is the job of the DPWH; monitoring and prediction of natural disaster causing phenomena are doneby the PHIVOLCS and PAGASA; contingency planning, response and recovery have been entrusted to the DCCs; rehabilitation and reconstruction are supposed to be the responsibility of the line agencies concerned with the impacted sectors-- the DPWH for damaged infrastructure, Department of Agriculture for impacted agricultural areas, Department of Trade and Industry for impacted industrial sectors, etc. with the NEDA coordinating the planning and monitoring. During the past three years, however, the practice has been to create inter-agency task forces, committees or commissions to handle disaster response, rehabilitation and reconstruction.

A new organization for disaster management would either takeover from the existing bodies the functions related to disaster management (and in the process render the existing organizations redundant), duplicate their functions or serve as an umbrella, coordinating or integrating entity to be superimposed on the existing. But why create another bureaucratic ladder? With some upgrading and priority reorientation the existing agencies could very well take care of hazards assessment and zoning, land use planning, development and building design and regulation, and the establishment disaster protection structures. Disaster is just a temporary disruption of development or constitutes the other face of development. The most logical organizational alternative would be to integrate, into the mandates of the development planning and implementation institutions the responsibility over the long term pre-event as well as the reconstruction or redevelopment aspects of disaster management.

For the contingency planning, response and recovery aspects which appear to be the weak link in the disaster management continuum, the not-too ad hoc yet not-too permanent, and coordinating DCC set up is still a logical choice. Unless a country chooses to remain vulnerable forever, disasters should be dealt with as non-permanent occurrences. The ultimate goal of proper disaster mitigation measures like land use planning and control, disaster- resilient structure design and construction, and protective structures, is to significantly reduce, if not phase out, disasters and hence, the need for contingency planning, response and recovery. Meantime, while these long term mitigation measures are being developed, the entity for contingency planning, response and recovery would have to be provided with adequate equipment, trained manpower, funding and authority to plan for and respond to disasters.

On division of disaster management responsibilities among the various levels of organization

Hazards assessment and zoning, monitoring and prediction which require highly technical expertise and research inputs will have to remain in the hands of national technical agencies. But the enforcement and adoption of mechanisms for implementation of zoning rules and regulations as well as the transmission of warnings should be the responsibility of civilian officials. Land use control and management could be a shared responsibility between the provincial and municipal/city governments. While the setting of standards for building design and construction should be undertaken at a national level, enforcement could be best ensured at the local level.

Preparedness planning should proceed from the lowest level to the highest level applicable for each hazard. Barangays and municipalities which are disaster prone should be encouraged to adopt contingency plans.

One issue raised by the NDCC is the need to decentralize operations and to build up the capability of the lower levels to be self-reliant. This was made glaring by the experience of Baguio City which was, for several days, cut off from the rest of the world by the disaster-with power and communications knocked out, transport routes blocked by landslides and fissures and the lone airport damaged. A number of villages were also isolated and rendered inaccessible by landslides. In such situations, a self-reliant disaster response body, would be most appropriate. The logic of this seems irrefutable, but the limitations to the capability of small communities to prepare for and handle disasters, must be recognized.

Barangays and small towns could stock up and prepare for disasters to enable them to provide for the basic needs of their inhabitants for a certain period of time, say, one or two weeks. They may also be expected to do some rescue and recovery work. Households and communities at the barangay level have been found to be quite capable of rebuilding damaged houses and attending to their immediate basic needs. Disaster response organizations (government and NGO alike) have, however, tended to overemphasize and overdo the provision of relief from outside.

Where the impact of a disastrous event is widespread and extensive., rescue and recovery work (such as extraction of vicunas from collapsed structures or ravines, road clearing, restoration of communication and transportation services, restoration of power and water supply ) require the use of heavy, costly and sophisticated equipment in which small towns and barangays cannot be realistically expected to invest. Rescue and recovery work especially in earthquake-caused disasters, likewise require special skills. Hence, these tasks would be more appropriately assigned to the cities or regional capitals. In disasters involving more than one region, the national bodies would have to be mobilized.

Rehabilitation and even reconstruction or redevelopment could be left to the various local government bodies concerned with some financial and technology assistance from the national government.

On the role of NGOs

Many private and non-government organizations indeed contributed to the operations by donating and distributing relief goods, providing transportation facilities, manpower, communications, medical treatment, first aid and rescue services and assisting in rescue operations throughout the disaster area. But there were so many of them and their sudden convergence in the disaster areas as well as the practice of manys NGOs of directly distributing the goods/assistance to victims without coordinating with the DSWD or concerned government unit, added to the confusion and encouraged the unscrupulous inhabitants to take advantage of the situation.

The NDCC recorded some 85 foreign-based and hundreds of locally based NGOs that were involved in the disaster operations. In Union alone, the DCC listed more than 50. NGOs mosty Philippinebased that worked in the province, In Benguet, the council reported more than 25; in Cabanatuan and Dagupan there were as many or even more though no systematic listing was circulated by the cities* councils.

An official of the JVOngpin Foundation Inc., an NGO, recounted that the "victims" had two ways of maximizing from relief distribution; family members fanned out to the different distribution centers; and family members changed their family names when submitting themselves for distribution lists. Consequently, the more aggressive relief seekers got the most of the relief while those in the less accessible areas got little to none at all.

In a meeting of NDCC (Minute, Sept. 27, 1990), General Abat reported that during the height of the July 16 earthquake, the NGOs were not coordinating with the e government agencies.

Towards the latter part of July, however, some NGOs started getting together and coordinating with government units. In Baguio, the NGO members of the DCC formed an ad hoc umbrella organization. In La Union, the NGOs there likewise organized themselves under one umbrella organization--the PANGOLU.

Some NGOs, however, persisted in doing their own thing; and stayed outside the umbrella organizations. One year after the earthquake, some communities visited by the PHIVOLCS, survey group were still receiving relief goods from NGOs.

NGOs could be integrated into the overall disaster management function provided their role is clearly defined and mechanisms for coordination with the government would be effected so that they would not duplicate or even usurp functions that should properly belong to the public sector or to the affected communities. Also, measures should be adopted to identify legitimate or genuine NGOs from fake ones which have been taking advantage of disaster situations to make profit or advance their private interests.

The July 1990 earthquake disaster showed certain areas of disaster management activity wherein NGOs could be most effective. In coordination with the government, genuine NGOs could be made principally responsible for provision of disaster relief and assistance. The Red Cross has consistently played this vital role. As principal relief providers, NGOs should likewise be actively involved in contingency planning.

In Dagupan City, a militant NGO acted as pressure group which worked for the speedy release of rehabilitation funds and monitored the implementation of the rehabilitation projects to ensure that these were done punctually and properly. This role of fiscal monitor could indeed be effectively assumed by NGOs not only for rehabilitation projects but also for development and mitigation projects.

However, the government should think twice before turning over to the NGOs the task of implementing rehabilitation, development and mitigation projects. NGOs are becoming such as administrative and political fad that there has been an increasing tendency on the part of the government to rely on them for tasks which the bureaucracy is being paid to do and is quite capable of doing. One result is an underutilized bureaucracy. The much publicized efficiency and managerial skills of NGOs have also been put to question by the miscarriage of some projects assigned to NGOs recently.

A cursory review of the composition, leadership and actions of the NGOs that have been emerging lately reveals the growing influence of the elite and vested interest groups, belying the claim that NGOs embody or articulate popular/mass sentiment or will. Passing on development projects to such NGO fronts of vested interest groups might betray public interests which the people entrusted to duly elected government officials.

BIBLIOGRAPHY

"A time to build, a time to help'". Manila Chronicle. July 20, 1990.

Aquino, Corazon C. 1990. Administrative Orders: AO 183, July 17, 1990; AO 184, July 18, 1990; AO 185, July 20,1990 and AO 189, July 30, 1990.

Benguet Regional Disaster Coordinating Council, 1990. Minutes of.Meeting. July 20,1990.

Cruz, Neal H., 1990. Lasting images of the earthquake. Daily Globe. July 23, 1990.

Editorial. Malaya. July 19, 1990

House Of Representatives, 1990 , 1991. House Bill Nos. 22363, 31321, 315717, 32997 and 312110.

Hundreds still trapped. Philippine Daily Inquirer. June 18, 1990

National Disaster Coordinating Council (NDCC). 1990. Minutes of Meeting. August 10, 1990 

________. 1990. Preliminary Report on the July 16, 1990 Earthquake. August 21, 1990.

________. 1990. Minutes of Meeting, September 27, 1990.

________. 1990. Final Report on the.July, 16, 1990 Earthquake. Nov. 14 , 1990

National Economic And Development Authority (NEDA). 1990. Reconstruction and Development Program.

Olivares-cunanan, Belinda, 1990. Structures must comply with Building Code. Philippine Daily Inquirer. July 20, 1.990.

Puno, Ricardo V., Jr., 1990. Are we ready for another bid; one. Philippine Star. July 1.9, 1.990.

Rescue proceeds slowly. Manila Chronicle. July 18, 1990

Sicam, Paulynn P., 1990. Tremors that rock our complacency. Chronicle Magazine. July 22, 19901

Soliven, Max, 1990. A time of crisis separates the heroes from heels. Philippine ,Star. July 22,1990.

United Nations Centre For Human Settlements (HABITAT) Expert Mission. 1990. Technical Report on Luzon Earthquake of 16 July 1990, Republic of the Philippines with Recommendations for Reconstruction and Development.

United Nations Disaster Relief Organization (UNDRO). 1986. Disaster Prevention and Mitigation: Social and Sociological Aspects. Vol. 12.

Villanueva, Hector R.R. 1990. Wrong Priorities. Philippine Daily Globe. July 23, 1990.

APPENDIX 1

Some Media Comments on Government Response to the July 16 Earthquake

"Rescue efforts were disorganized...Using nylon ropes, steel bars, sledgehammers, chisels, automobile jacks and even bare hands, rescuers worked through the night and the whole day yesterday but made little progress. More sophisticated equipment and more experienced hands still had to arrive"- Hundreds still trapped, Phil. Daily Inquirer, June 18, 1990.

"Much of the rescue effort was uncoordinated and disorganized and lacked the necessary heavy equipment to shift the debris ...In Baguio, rescuers were additionally hampered by power failures ...In Cabanatuan, rescuers working can the Christian Colleges used hammers, chisels and jacks."- Rescue proceeds slowly, Manila Chronicle, July 18, 1990.

"The immediate task is the rescue and feeding of the survivors. Three days after the earthquake, the abject failure of the government on this score is appalling". Editorial, Malaya, July 19,1990,

"The most obvious fact that has come out of this major earthquake is that we are woefully unprepared for natural disasters of major proportions... Reports were filtering in of rescue operations being conducted by well meaning and highly motivated workers who were apparently poorly equipped and who didn't have too much of an idea of what to do next."Puno, Jr., Philippine Star. July 19, 1990.

"One of the impressions left by the earthquake in its aftermath was the weakness of government to immediately take control of an emergency situation . Government seemed itself too numb to respond to the gigantic crisis; it was, in fact, the private sector which initiated the initial reactions." time to build, a time to help. Manila Chronicle, July 20, 1990.

"The recent disaster, which took many lives mainly due to the collapse of concrete structures, underscored the woeful inadequacies of our country in terms of sophisticated equipment fear handling fallen concrete slabs, boring through them and detecting life buried beneath the piles. Our equipment are not only inadequate but so primitive"- . Olivares-Cunanan, Phil. Daily Inquirer, July 20, 1990.

"What dismays the nation is the mounting evidence of lack of coordination and lack of will on the part of our own clumsy government to cope with crisis ...Worry that our leaders have not led in this hour of deepest tragedy and continue to waffle in their duty'"- Soliven, Philippine Star, July 22, 1990.

"Rescue efforts were uncoordinated, evacuation shelters non-existent. There were few basic supplies, such as food and medicine. People listening to their radios got more information and advice from private stations than from government". Sicam, Chronicle Magazine, July 22, 1990.

"What is more deplorable is disorganization, lack of planning and the insufficient importance given by the government to disaster control, science and technology transfer, and basic research in natural phenomena that the Philippines is especially vulnerable to, such as earthquakes, hurricanes and volcanic eruptions" (Villanueva, Phil Daily Globe, July 23, 1990).

On red tape

"There are many people, Filipinos and foreigners ready to help with donations, but what does our government do? Put red tape in their way. You have to get permission to even ship your donations which would still have to undergo more red tape at customs before they are released for shipment to the local government officials who would distribute the relief goods to the victims". N Cruz. Daily Globe, July 23, 1990.

Antonio P. Perlas, M.D.
National Program for Mental Health
Department of Health

 

On July 16,1990 at 4:26 p.m. an earthquake occurred which delivered one devastating blow that significantly affected six provinces and involved 1.2 million people. The destruction ranged all the way from the collapse of high-rise buildings, dwellings, and school houses to the breakup of highways; to landslides and cracking of earth surfaces; to flooding of farms; and to the injury of innumerable people and the death of at least 1,100 victims.

The physical desolation that followed forced its presence into the consciousness of a stunned nation, and everybody jumped to contribute what he could to help. The physical destruction, which was readily seen and thus more dramatic, was easily captured by mass media and projected to the rest of the country. There were, however, changes that occurred in the inner recesses of the victims that were not as obvious but were nonetheless important. These were the psychosocial consequences that necessarily accompany any sudden, significant disruption in the established relationship and activities of people.

The necessity of helping the hungry, sick, and homeless, was easy to understand: They needed very concrete interventions that everybody could relate to. Thus, widespread participation was generated in bringing this kind of help.

The psychosocial trauma, on the other hand, was more hidden and subtle. Being so, it was very difficult to identify and, on occasions, difficult to understand and empathize with. However, if no action is taken to prevent, minimize, if not altogether eliminate the abnormal manifestations of this trauma the psychosocial stresses could lead to a disability far worse than the consequences of a physical dislocation. I am sure there will be no disagreement if I were to say that the common pathway, after all, of all the physical effects of the earthquake is ultimately man himself, with all his feelings, emotions and consciousness. Thus, ultimately, man must be the focus of aid and rehabilitation.

These insights were not lost to President Corazon Aquino who on July 20, 1990, after visiting the earthquake-destroyed areas, convened a group of behavioral scientists to specifically address the human side of the disaster. This gave rise to the creation of the Mental Health Task Force on Disaster under the National Program for Mental Health. The activities of the Task forces were thereby coordinated under the structure of the Department of Health. Its mandate is to assess the psychosocial effects of the earthquake and to design and implement intervention packages so as to prevent the development of abnormal reactions and manage those that have already arisen.

Now, let us go into the psychosocial consequences of the disaster.

After an extreme life experience such as a disaster, one can expect an immediate and normal psychological stress response. As a consequence of the earthquake, there were loses: of loved ones, of properties, of livelihood, of community relationships, of heritage and others. These losses created an inner disequilibrium and feelings of fear, helplessness, dependency, and sometimes anger rooted in a deeper loss -- the loss of control over one's life and one's destiny. This loss brings about bereavement. Figure 1 shows the typical grieving process that we can expect under such conditions. It divides the whole process into (1) the event itself; (2) the aftermath; and (3) the recovery period. Note that during both the event and its aftermath, lack of control is present: This, in fact, is the one overriding characteristic of any disaster.

The graph shows that, as a consequence of a loss, there is a downward swing of the curve indicating a decrease in the energy available to the individual. The characteristic reactions are shock, denial, panic, numbness, bargaining, avoidance, fear, and helplessness. This is also accompanied by a disruption or deterioration of ordinary life activities and some physical symptoms. At the moment of and a few seconds after the earthquake, we may have found our minds going blank or racing furiously trying to think of what to do. Perhaps there was a moment when we were a bit confused or unable to concentrate. These are all normal cognitive expressions of the stress response that one can expect in situations like this.

Soon after the event, during the aftermath, as shown in Figure 1, there us an upswing of the curve signifying an upsurge of energy. There is an emotional release, misdirected anger, and a splurge of energy and emotion. This is the period wherein there are such manifestations as excessive chatter, uneasy laughter, undirected or purposeless activities, and blaming of people or institutions for the person's sufferings. It is at this point that people get angry with the government, with the church or any other agency for not being organized or responding quickly enough to the disaster as they give vent to this upsurge in energy. This was the stage of a man that our group saw in Cabanatuan. He is a member of a clan which lost 19 of its members in the earthquake. He was seething with anger and could find no relief for his tension. He blamed everything and everybody including those were considered by some of the people in Cabanatuan as heroes. He saw in the identification and honoring of some, the ignoring or rejection of others.

However, as time wears on and there is no Relief, the curve slowly goes down bringing out again the sense of helplessness with resentment, depression, withdrawal, unresolved feelings, and hopelessness among others...During this period, what has been termed "survivor guilt" emerges. "Why did I survive?" or "Why did they, and not I perish in the disaster?" are questions asked during this period. We have school teachers who do not want to ever teach again because it happened that they were not inside the buildings when they collapsed and claimed the lives of their students. Of course, there are other forms of guilt. A teacher was inconsolable because she was instrumental in getting many children enrolled in a school that collapsed.

Going back to the graph, we can see that after the aftermath, there is a period of recovery. With recovery, there is a regaining of control. Recovery starts with the self, followed by the family, and then the community . So the recovery process starts with the self and moves on to the community. This is a very important process to remember since it will have critical implications on intervention strategies.

Table 1 shows some of the typical acute reactions to stress. these are subdivided into physical, emotional, and cognitive and behavioral symptoms. These are manifestations that we can see whether the stress is a near-miss car accident, a typhoon that results in the drowning of many people, or the earthquake that occurred on July 16,1990.

As you will notice in Table 1, stress brings about physical symptoms such as increase in heartbeat and respiration, elevation in blood sugar level, increase in perspiration, and slow digestion. The emotional symptoms, on the other hand, include fear, anger, and frustration. The cognitive and behavioral reactions consist of the actions we take to solve the problem. As stated earlier, however, the mind may become blank or get confused.

In psychiatry, the further aggravation of a normal response to a disaster which could lead to a psychiatric illness has been termed Post-Traumatic Stress Disorder (MD). Some. of the symptoms associated with this are hyper-alertness, exaggerated startle response, and difficulty in sleeping. And when one finally gets to sleep, recurrent nightmares occur during which the traumatic event is relived over and over again.

All these are powerful emotions produced by powerful disruptions to our ordinary lives. Unless these emotions are handled properly, they could lead to long-standing disability and personality difficulty. Table 2 lists the chronic reactions to stress. The categories follow closely those of Table 1 except for an added dimension of spiritual reactions. It will be noticed in the enumeration that there are many possible consequences of a crisis or disaster should the individual continue to be exposed to the disruption and its aftermath without arriving at a resolution. It must also be pointed out that the aberration, if left unattended, becomes more deep-seated in the long-term, affecting the very personality structure of the individual. As shown in Table 2, some of the personality disruptions are declining interest in others, doubt of value systems and religious beliefs, questioning of major life areas, and disillusionment.

Thus, we must be able to cope if we are to proceed to the phase of recovery where the most important accomplishment is to regain control. Ultimately, the person accepts the loss and finally lets go of a loved one, whether it be a person, a possession, or a heritage. As one person who grew up in Baguio poignantly stated, "Baguio will never be the same again. I shall never recapture my lost childhood "

Luckily for most, this recovery occurs spontaneously. We Filipinos are specially fortunate because we have extended kinship relationships on which we can fall back for emotional support.

As I said earlier, recovery starts with the self, leads to the family, and finally leads to the community. Thus, it is important that we address the individual's needs first and foremost if we hope to be able to establish a sustained and relevant rehabilitation of the communities affected by the earthquake.

But who are the people whom we should seek out? Who are the victims? The direct victims are easy to identify since they are the ones entombed inside a collapsed building or those injured, or they are the parents and relatives of the dad and injured. Certainly, the parent who lost 6 of his 7 children in the school reduced to rubble in Cabanatuan is a direct victim. His 7th child did not perish because he was only 6 months old. But beyond these direct victims are the indirect victims. These people, although not personally affected by any loss, nonetheless shared in the tragedy of the moment. I believe this will involve all those who read about the disaster or listened to the almost hourly report on all the miseries occurring in the affected areas. Although the emotional stress of these indirect victims is not as great as that of the direct victims, nonetheless they must also be recognized as victims because they may also develop some psychosocial reactions to the disaster.

Finally, we have the hidden victims. These are the care givers who are busy helping others. They look like the paragon of strength, fulfilling the dependency needs of those who are unable to cope. An example of this is the midwife who single-handedly evacuated a whole barangay to higher grounds during the earthquake and who remained for two days the people's sole anchor as they starved in the evacuation site. She maintained a stoic bearing, believing that it is not good for her to show any sign of "weakness" by giving vent to any emotion. It was only when she participated in a group intervention handled by Task Force and found out that it is all right to have emotional reactions to the disaster that she let go and cried interminably.

Crying was an opportunity to release pent-up tension which would otherwise have resulted in some disability in the long-term. This time, she was consoled by the other midwives in the group.

Hidden victims are usually not recognized as victims. They are the rescue workers who have been exposed to all the injury and death as they try to out bodies. They are the health workers: doctors, nurses, and other paramedical professionals who take care of the sick and the injured. They are the teachers and social workers who try to care for those who try to regain their lost anchors. All these care givers, after so much exposure, develop what has been termed a "burnoutsyndrome"which is predominantly characterized by exhaustion and depression but also sometimes with manifestations of a post-traumatic stress disorder.

This burnout phenomenon is apparently so pervasive that among the Ifugaos they even have a ritual to relieve people of this. I read somewhere that the Ifugaos lave a ritual called "duo-es" which must be performed for those who have plug out a dead body to stop their nightmares. The nightmares sound like a post-traumatic stress disorder and the Ifugaos have their own version of psychiatric treatment, I believe it is important for: us to know more about this and other similar practices that are truly Filipino.

In addition to the stress arising from exposure to injuries and death, the care givers may have the second stress of being direct victims themselves. The first thought of a social worker in Dagupan was how to give relief goods the victims. She half-forgot that her own ifamily was also victimized. A sanitary inspector in La union burst out crying as instructions were being given on need to build latrines because she was worried about her children who were also in die in distress.

The stress if care givers may be severe. Three months after the California earthquake, there was a four to fivefold increase in consultations for psychosomatic illnesses among the rescuers and the number of applications for a change of job rose abnormally high.

A look at how victims are responding away be glimpsed from a preliminary analysis of the answers to the self-rating questionnaire (RCI) administered to students in Cabanatuan which revealed a 94.08% presence if symptoms among 355 persons in one group and 78.55% in another group of 387. This can be seen in Table 3. Actually, the first group are the stu dents from the CPP and the second are students from another school which did not collapse. It is interesting to note that even chose people who were not involved in the collapsing of a building also suffered a tremendous amount of symptoms or disturbance. The most common symptoms noted were physical symptoms like fatigue, headache, sleeplessness, stomach discomfort, and poor digestion. Also noted were emotional/cognitive reactions like depression, fearfulness, nervousness, difficulty in thinking and making decisions, and suspiciousness. Table 4 shows the common reactions of the students tested in Cabanatuan. As you will notice, the symptoms of the students are similar to the usual symptoms of the students after a disaster which was discussed earlier.

These findings show how very important it is to institute some active interventions to prevent the occurrence of more severe psychological impairment and help the victims resolve their psychosocial reactions.

In designing the program of intervention, we took into consideration the following guiding principles (see Table 5):

1. There is a variety of psychosocial reactions to the earthquake, ranging all the way from normally expected changes to the more severely manifested psychological aberrations.
   
2. This being the case, there is a need to offer several forms of interventions requiring different skills and levels of specialization. Particular consideration is given to-the design of a module that addresses our unique cultural distinctions.
   
3. There is also a need to reach out to as many people and in as quick a time as possible since the time within which psychosocial support is given is critical in achieving the desired results.
   
4. In doing this, care must be taken to match the psychosocial need of a person with the help being offered. Thus, case finding must go hand-in-hand with, the provision of different types of psychosocial services. The process of relating one to the other should be put solidly in place in the shortest possible time.
   
5. Should it happen that the needs cannot be matched by the resources at hand, there should be a referral system that can be activated.
   
6. Care should be taken to organize individuals in the provincial areas belonging to different sectors and to train them sufficiently so that, at a certain point in the future, these individuals can take care of the needs of the area sufficiently. This institution building is critical because the ultimate aim of the Mental Health Task force on Disaster is to create a systems at the local level that should be able to sustain itself, not only to answer the psychosocial problems created by the earthquake but also to respond to other similar needs that may happen in the future.

   We believe that this is one of those instances when a problem has been turned into an opportunity and an event which could prove devastating has been turned around to spur development.
   

7. Because of the enormity of the problem, the Mental Health Task Force on Disaster, which started as a small group, should expand exponentially and function within a well-established government structure dedicated to service. It is in this context that the Task Force quickly became a multisectoral and multidisciplinary concern involving not only psychologists and psychiatrists but also social workers, spiritual counselors, family therapists, and other similarly minded concerned professionals coming from the academe, the government and non-government sectors. Each one contributed his own skills, expertise, and insight into a program which will be described later by Dr. Ignacio.
   
8. And finally, the documentation of the process, which is a special concern of the Secretary of Health, has to be institutionalized so that we can learn from our experience and establish an institutional memory.

The next figure (Figure 2) shows in a diagram, the series or cycle of interventions. It shows the overall strategy that we adopted and the different levels of interventions.

As can be seen in the diagram, we started with what we call a process - the Critical Incidence Stress Debriefing or CISD Intervention. This will be discussed in greater detail as Dr. Ignacio describes the implementation of the program. Suffice it to say, however at this point, that this procedure is used for training as well as for giving the psychosocial support needed by the victims. With the Critical Incident Stress Debriefing, one can develop subtrainors and, at the same time address the needs of the victims, who may be direct ones or hidden ones. This process, however does not preclude shortcirculating the cycle so that a person can go directly into the more intensive program when needed, as shown in Figure 3. The victims can either. have only one or several CISD interventions before becoming well, or they may need more intensive .treatment including medication. The progress of these people will be followed up and monitored.

Let me point your attention to some of the features of the cycle of intervention as shown in Figure 2.

1. The training of subtrainors is an ever-expanding circle. The subtrainors themselves train other subtrainors. This is the way we try to rapidly expand the circle of people who are able to attend to the problems of disaster. Four things, however should be closely monitored:

   1.1 The qualification and background of those chosen to "'subtrainors."

   1.2 The certification of those who will be allowed to train others. In this particular instance, they can either just help the victims or become trainors themselves. But training requires special skills and to be able to do this, the candidates must first be certified.

   1.3 The maintenance of a level of quality in the conduct of the CISD.

   1.4 The proper identification of those who will need more intensive intervention. Subtrainors should have the capacity to identify the victims who will need more intensive intervention.
   

2. Victims may require one or more exposure to CISD depending on the need of the individual.
   
3. The system provides for different kinds of interventions ranging from CISD to the more intensive therapy not necessarily done by psychiatrists, to psychiatric intervention and medication.
   
4. There is continuous monitoring and documentation of the processes as well as the outcome of the intervention to ensure quality as well as provide a basis for expanding our knowledge anal understanding of the psychosocial issues in disaster.

Figure 3 indicates how victims are identified. This, actually, is a recapitulation of Figure 2, except that this follows the different steps that a patient can take. He is perhaps referred by a group or a government agency. He goes through a CISD and is identified as a person needing no more intervention or referred for more intensive treatment.

The mass media also informs people who are then able to identify themselves or others as victims needing CISD intervention or a more intensive kind of treatment. Finally, we have the trained "subtrainors", conducting discussions at the community level, who might be able to identify and then refer victims for more intensive treatment:

Taking all these into consideration, the Mental Health Task Force on Disaster went out to do its job fully aware of the enormous responsibilities that lie ahead-The work cannot be done by us alone. Its concerns do not belong only to the province of the social scientist but to all of us ordinary Filipinos who must bear the burden of the devastation and emotionally support each other in this time of trial. I am sure, however, that given the strengths of the Filipino, this moment shall prove to be both a challenge and opportunity for development.

Lourdes Ladrido-Ignacio, M.D.
World Association for Psychosocial Rehabilitation for the Western Pacific

In the northern part of the Philippines, panic-stricken people of all ages and from all walks of life ran for their lives as the earthquake, with a maximum intensity of 8 (adapted Rossi-Forel Intensity Scale) struck. They screamed, cried and watched in disbelief as buildings collapsed entrapping and killing adults and children. After two days, the cities of Baguio was in ruins, Dagupan was submerged, and Cabanatuan had the stench of death. Soon, the count placed the confirmed dead at 1200. It was feared that many more bodies would be found as rescue work continued. Rescue operations, however, were severely limited because continuing landslides cut off access to the disaster sites. Those in the unaffected areas watched with great sadness, and concern: soon they organized themselves to provide emergency relief, food, and shelter.

The Mental Health Task Force on Disaster of the Department of Health was organized in response to the call of President Corazon C. Aquino to give immediate attention to the psychosocial consequences of the disaster. After a visit to the devastated areas, the President was convinced that the disaster caused overwhelming psychological distress that might lead to far- reaching psychosocial damage on the lives of the victims. She also recognized that those who survived were just as traumatized.

As suggested by the President, a team of psychologists and psychiatrists under Task Force on Disaster was immediately sent to Baguio, not only to buffer the emotional shock that was still raging on, but also to plan possible areas of intervention. This paper will present the psychosocial interventions so far undertaken by the Task Force. We started by sending several teams to Cabanatuan City and the province of Nueva Ecija, Dagupan City and the province of Pangasinan and Aringay town (in La Union) and most of the other towns of La Union. We could not follow through with Baguio at that time because Baguio was inaccessible due to landslides and air transport was limited to food supply and rescue operations. We also covered the town of Tarlac and Nueva Vizcaya. In those activities we provided the necessary crisis interventions to buffer the shock. We also continued the process of psychosocial management even through the recovery and rebuilding phases. Definitely, the human factor is just as crucial as the reconstruction of roads and buildings.

As we in the Task Force discussed and planned our work, we faced another crisis. We knew very little about what we needed to do. None of us had previous experience in handling disasters. We undertook the task only with the compelling desire to help and be one with the victims in their suffering.

It has been gratifying to know that many colleagues in the field were ready to collaborate with us. Through our pooled efforts, we evolved strategies for intervention which we then applied. An expression of gratitude to colleagues who have labored and traveled to Baguio, Cabanatuan, Dagupan, La Union and possibly through the landslides of Nueva Vizcaya may not even suffice at this point.

BASIC PRINCIPLES

The Task Force's guiding principle was that stress is an extreme life experience outside the range of usual human experience and markedly distressing to almost everyone. This results in an intense arousal felt as psychological distress-feelings of fear, depression and anger, or denial or numbness of feelings. These adaptive reactions do not generally lead to psychologic illness: only a minority do. Whether or not illness follows depends on two factors related to vulnerability: the social support system and the personality factor before and during the distress (Figure 1).

Another principlewe considered is that the psychological response following an extreme life experience is immediate, expected, and "normal". The response is not unique, rather, it is shared by many. The responses are not symptoms of psychiatric illness, and majority of victims do not develop any illness. Bereavement is a vital, pervading experience because of the experience of loss. Grief is experienced because of loss through death, loss of a body part, loss of property or livelihood, or loss of one's social role, may compound the psychological impact of the disaster.

Psychosocial concerns can be identified as early as the impact phase of disaster and proceeds throughout the phases of recovery and rehabilitation. Crisis interventions are, therefore, appropriate during the phase of inventory of the consequences of the disaster all the way through rehabilitation. Appropriate and immediate interventions are crucial because of their vital, facilitative and preventive functions.

We felt that, because most of the recipients of interventions are normal, there is a need to avoid mental illness labels. Descriptive terms, not professional jargon, are therefore used to identify individuals. We call them "victims" instead of "patients".

OBJECTIVES FOR THE INTERVENTION PROGRAM

The following are the objectives of the psychosocial intervention program we implemented:

A. To help the victims

1. Re-establish equilibrium and harmony after the disaster through:

1. Expression and release of feelings and emotions, while recognizing and accepting that these are valid and normal,
2. Acceptance that, they must undergo a period of grief for the losses they suffered without the necessity of totally losing control; and
3. Identification of coping, mechanisms which they have applied and used to gain strength and a sense of competence, 

2. Regain personal control by allowing them to plan for their future.

These activities are basically directed towards the self. The initial attention towards the self allows one to go beyond it and help others. This latter condition is crucial during the tasks of recovery and rehabilitation as the victims resume their daily lives and participate in rebuilding their communities. 

B. To provide continuing consultative service try those found to have psychological illnesses.

STRATEGIES FOR INTERVENTION

The Following are the strategies for intervention that a used in tire, areas eve visited:

1. Psychosocial processing through the Critical Incident Stress Debriefing (CID); 
2. Efforts at community involvement; and
3. Education and information campaign.

1. Psychosocial Processing

The Critical Incident Stress Debriefing (CISD) has been adopted to provide direct psychologic intervention or the victims. It is a three-hour group session. It allows the ventilation and sharing of experiences, feelings, and reactions during the critical incident (the earthquake) and includes discussions on the meaning of the crisis for the participants. It allows sharing and discussion of the various coping skills that. the person used in reducing his or her stress. It further allows the formulation of contingency plans so that, life wild go on.

The CISD experiences we have had are beyond words. The emotional experiences shared were so powerfully charged, yet the group process seemed enough to provide the participants in the session with a chance to ventilate and defuse. their feelings, they found relief in the realization that they have not been alone. The group process showed the, participants they have some degree of personal control and capacity for recovery. At the end of the three hours, this sense of control was somehow felt as real and the participants proceeded to plan for the days ahead. I cannot forget. a parent who said: "Ako mismo ang naghugot ng anak ko. Nag-iiyaak ako. Para akong loko-lokong nagsisigaw sa plaza. Kalalaking tao ko, umiiyak ako. Umuwi ako sa bahay para tingnan ko ang ibang anak ko. Noong makita kong ayos sila, nagdasal na lang ako. Nangako ako na bibitawan ko na ang querida ko. Sinisi ko ang sarili ko at ako buhay. Binigay ko na lang ang lahat sa Diyos. Hurningi ako ng patawad. Nagpasalamat na iniligtas kami. At hindi na ako natakot. (I myself pulled out my child. I shouted at the plaza like a madman. I cried, an unmanly thing to do, but. I couldn't help it. I went home to look at my child. When I saw (him/her), I could not do anything but pray. I promised to let go of my mistress. I blamed myself for remaining alive. Finally I surrendered everything to God and asked for forgiveness. I thanked Him for saving the rest of my family. And then I was no longer afraid.)"

Our present experiences have, led us try modify the CID, which was adapted from Western models with the incorporation in the group process of the affirmation that the varied responses and coping mechanisms to acquire psychological strength and mastery in each participant carry prominently a spiritual dimension, i.e., the experience of God during and after the crisis. That they have called on Him, that they have prayed and found strength, that they have acknowledged God's power in their lives. Among the techniques in relaxation adapted is prayers done vocally or through quieting down activity. During this time each participant acknowledges the ability to relax when given the opportunity to touch base with God within who is the source of strength and life.

The healing effect of this activity has been acknowledged repeatedly during the CISD sessions. We believe that this has made the debriefing sessions for adults and children in the disaster areas culturally relevant. Prayer as truly a Filipino's source of strength in a crisis. This experience is truly Filipino fear every Filipino prays. And every Filipino finds prayer as powerfully strengthening. The debriefing has also facilitated the identification of high risk individuals and groups who will need intensive care like psychiatric treatment.

2. Community Involvement

We have also gone on to involve the community. Our effort is multisectoral and collaborative to reach greater number of the population. It includes community organizers, barangay midwives, school teachers, guidance counselors, social workers, local leaders and priests.

3. Education and Information Campaign

The last strategy would be the, information and education campaign. One approach is the distribution of leaflets about the earthquake and on how parents can help their children. These leaflets have now been translated to Tagalog, Pangasinense, and Ilocano. These were sent through people who went on a medical mission or inserted in relief goods packages distributed to the affected areas, rough these, the devastated arias have been reached.

Another approach is to educate the public on the psychosocial aspect of disasters through radio programs, television, and newspapers, Immediately, the leaps were used in than nationwide as well as local radio programs. A television program was to assisted an presenting the psychosocial dimensions of the disaster. Video-tape copies of this program have been made for future educational activities.

DEFINITIONS

1. Victims

Victims are adults and children who have been affected physically, psychologically and socially by the disasters apse are further classified into:

1. Direct victims Y those who were in the disaster area and who have suffered losses, bodily injuries or loss of body parts, property, livelihood, etc.
2. Indirect victims - those who were in the area of the disaster but suffered no particular experience of loss, etc. This is the general population.
3. Hidden victims - those who have to attend, take care and provide for the needs of direct victims. These include relief and rescue workers and emergency caregivers like medical and nursery personnel in the hospitals.

2. CRITERIA FOR HIGH RISK

When we intervene, we apply certain criteria to identify victims who have a high risk of developing psychosocial problems. These criteria have guided us in identifying priorities for intervention.

The following are at high risk for developing psychosocial problems after the disaster:

1. Those who were trapped or entombed in destroyed buildings, with or without physical injury.
2. Those who watched a friend or relative die during and after the disaster,
3. Those who were displaced (from house/school) after the disaster.
4. Those who suffered the death of at least one member of the family.
5. Those who do not show psychological symptoms or would show symptoms that are prolonged or distorted.
6. Those who had previous crises in their lives before the disaster, like unemployment, interpersonal conflicts, academic failures, etc.

THE INTERVENTION PROGRAM

The intervention program in the disaster areas are conducted in several phases (see Table 1).

The intervention program in the area are conducted in several phases. The initial crisis intervention phase includes an initial consultative meeting between the Task Force local officials and identified mental health professionals. During these meetings, a CISD would be conducted with the group which results in a plan for psychosocial intervention after a three hour session. Often, as crisis intervention is planned, local manpower resources to collaborate and undertake psychosocial intervention with the Task Force Teams are identified. These local professionals are then trained as CISD facilitators because they are expected to echo the CISD to the victims in their areas of work. Initially, the Manila team co-facilitates the session with them until they feel competent in facilitating. In some areas, linkages between sectors have resulted in facilitating the sessions. As a consequence, coverage for interventions has been faster. The collaboration between teams from Manila and from the local areas have reduced the problem of burnout. This scheme has been followed in all the areas and a multisectoral collaborative approach prevailed. The Mental Health Task Force teams have included psychiatrists, psychologists, family and pastoral counselor's and community organizers.

Interventions would also have to be set up for the high risk victims who would be identified at the time of the inventory of the consequences of the disaster, which oftentimes, is almost immediately after the disaster. Among the high-risk victims whom we have been reponding to are the students and teachers in collapsed schools. We have done that in Cabanatuan. We will probably be doing that still in the school in Aringay LaUnion. We have already started this phase in relocation centers in Dagupan and in evacuation centers in the same area. We have also identified and rnet with the parents of the dead students, We have gone into community work in the barangay affected by the destruction or in the cluster of households with deaths in the family. The strategy that was primarily adopted was the CISD. The victims often needed more than one CISD.

There were also other interventions like family counseling and advising the schools on psychosocial-oriented programs. Simultaneous with what we are doing to the victims. We have also encouraged the different groups to exercise community rituals and indigenous, coping practices. Some of these rituals included days of mourning, the Masses of mourning, the flag at half-mast and processions in some of the barangays. Educational lectures about tire earthquake and some of the normal stress reactions have also been done.

Later on, we will have interventions for psychologic morbidity. We do not anticipate this to be a very big task. Most of the earlier activities have already been directed towards this second level of intervention. 4e are moving to some of' the disaster areas for interventions fear those with psychologic morbidity. These are victims whose psychological symptoms have not abated at least six to eight weeks after they were identified as high-risk.

At this point in time, we have modified again the CI SD to make it an entry point for the group therapy counseling that would later be used. Medications have been started for some of the cases. Various forms of psychosocial treatments, from psychotherapy to behavior therapy to hypno-therapy are being planned.

Let me illustrate our psychosocial interventions by describing our actual experience in Cabanatuan City (see Figure 2 on Psychosocial Interventions in Cabanatuan City).

Twenty-four crisis workers from the Mental Health ask Force went to Cabanatuan on August 7, 1990 and gave CISD to a group of guidance counselors of Araullo University where the survivor students of the Christian Colleges of the Philippines (CCP) are now enrolled. Twenty of these guidance counselors were trained. At the same time, the crisis workers trained 8 technical staff of the Department of Education, Culture and Sports (DECS).

The trainees has been multiplying as the first trainees trained other people. The 20 guidance counselors of Araullo proceeded to train 73 faculty members. The latter, with the help of the Task Force members, have trained 2,167 students of Araullo and all the 733 students of were considered high-risk according to our criteria.

CISD was undertaken with these high-risk victims (aged 12 to 18) by the Mental Health Task Force led by one of the child psychiatrists. After one CISD, the high risk students of Araullo recovered. Among the CCP students, 69 out of 733 continued to show symptoms of stress. These 69 were given group counseling. After one or two sessions the group was reduced to 24. After 3 or 4 CISD's which now takes the form of therapeutic counseling, the group has further narrowed down 12. These victims are now being given individual therapy. As of September 18, 1990, 11 remain in this group. These victims are now being seen as child psychiatry or adolescent cases.

The original group of 8 trainees from the Department of Health has now grown to 15. The original group of 7 trainees from the department of Education has grown to 13. Thirteen hundred fifty seven have, been trained at DOH and 250 guidance counselors and teachers at DECS. All in all, 607 of DOH and DEC personnel have undergone CISD.

The groups are moving into the community. While the Task Force initially targeted the training of guidance counselors, teachers and health workers, 44 social workers from the Provincial Social Welfare Department and 35 family counselors from the Center for Family Ministries of the Ateneo de Manila University attended to the needs of parents or others with multiple losses, like the parent who lost six out of seven children and the clans that lost 13 to 14 children. Social Workers continue to provide relief and shelter to the victims. Again on August 30, 1990, the community suffered landslides caused by the aftershocks.

We know that the Task Force will not be able to personally reach all the people affected by the earthquake. Through their training in CISD, the DECS and DOH groups have become sensitized to psychosocial problems. They are expected to help the elementary school teachers, the midwives and the barangay health workers in reaching out to the victims because they have the most access to households in the barrios.

To summarize, in Cabanatuan, among the CCP student's, 722 of the original high-risk victims have recovered from psychological symptoms. Only 11, have been identified as cases after 1-1/2 months of CISD. Among the students of Araullo University, the 15 students identified originally as high-risk have all recovered.

We have moved into interventions in Baguio, Dagupan and La Union (Aringay). The results of intervention are as follows:

A. Baguio City

1. A core group with 26 multisectoral members was formed. This core group:

1. coordinates with agencies involved in psychosocial intervention;
2. initiates CISD in high-risk groups especially the school children; and 
3. gives proper information.

2. A series of CISDs for victims and trainors numbering 363 were conducted from September 10-13, 1990. The participants included cadets from the Philippine Military Academy (PMA), the religious, miners, social workers, DECS personnel and health officials. The cadets and the miners took charge of rescue work in the city. This has been nationally acknowledged as having succeeded in a high rate of rescue of living victims.

B. Dagupan City/Pangasinan

1. Linkage was established between DOH and DECS to implement the programs with community involvement.

2. Plans are being made for CISD for 268 direct victims and 6 hidden victims (social workers) in relocation centers.

C. La Union (Aringay)

1. A core group is still being organized through the Regional Health Office.

2. The students of the collapsed Notre Dame College have been identified as the priority victims for intervention.

3. A CISD is planned for 257 direct victims.

WHAT WE HAVE DONE SO FAR

1. With the help of local leaders and professionals, we have identified the individuals, groups and communities considered as high-risk for psychosocial problems and we have intervened at various levels.
2. Local professionals have been trained and assisted to become, crisis workers and to handle. highrisk victims.
3. Support has been provided to crisis workers including rescue and relief workers who are hidden victims of the disaster.
4. The Task Force has initiated the linkages between different agencies, DEC's and DOH„ so that the task of implementing psychosocial interventions can be integrated into the. system of services during disasters.
5. Training modules have been developed on the CISD for victims and for facilitators.
6. Leaflets have been produced on the earthquake which can be adopted as an information tool which are also relevant for other forms of disaster.

PROBLEMS ENCOUNTERED AS INTERVENTIONS IN DISASTER AREAS PROCEED

The Task Force is limited in manpower resources, as well as in mobility. Local manpower for mental health services is almost non-existent in the devastated areas. Manila-based teams have to be organized to initiate and provide the whole range of psychosocial interventions at the different phases.

Although, the Manila-based professionals have been fantastic in their willingness to collaborate and help, they too are limited by the demands of their own jobs in Manila.

During their visits to the disaster areas, the mental health teams try to implement all that can be done with each trip. Hence, we send out at least 20 in each team. Transport problems sometimes become overwhelming. So far, however, we have not yet canceled our schedules except when floods and landslides prevent us.

Most of what we have done, experienced and learned in applying a workable, effective psychosocial intervention following the earthquake can apparently be applied in other kinds of disasters like typhoons, floods, fires, wars and coup d'etats. The CISD can certainly be adopted by the National Disaster Center, the Department of Social Welfare and Development, the Red Cross, etc. because this debriefing is necessary and vital in the assistance of victims. The people struck and devastated by the disaster not only need to have food, clothing and shelter. They simultaneously react with distress and their resultant behavior will determine how the disaster will be coped with at impact and during recovery from it.

This fact is crucial in a country like the Philippines which is apparently in continuous disasters.

Arturo G. Corpuz
School of Urban and Regional Planning
University of the Philippines
Dilimann Quezon City, Philippines

1. LAND USE PLANNING VS. STRATEGIC PLANNING

Land use planning is a major concern of many urban and regional planners, especially those involved with government, because it is a direct input to the formulation of zoning ordinances and other land development regulations. It may be expected to become an even more active field of planning with the recent signing into law of the 1991 Local Government code, which decentralizes many planning functions and responsibilities to local governments. This means that more planners are going to be engaged in land use planning as the initiative and responsibility for this activity shifts from handful of national planning agencies to over a thousand local government planning and development offices.

Land use planning, however, because it deals primarily with the identification of broadly-defined activities for certain land areas, is unable to directly address earthquake-related disasters caused by the failure of specific structures. In effect, the standard land use classification (residential, commercial, industrial, etc.) does not distinguish among the individual abilities of buildings to withstand earthquakes and, it is indifferent to the varying degrees of disasters--from the minor to the catastrophic--that can take place during earthquakes. Although it can be useful, through zoning, in limiting the density of activities in areas identified as susceptible to earthquake-related disasters--in restricting liquefaction-prone riverine areas from being densely occupied, for example--it needs to be complemented by strategic urban and regional planning.

By strategic planning, I refer to planning that deals directly with the mitigation of earthquake-related disasters associated with, first, production and service networks that cut across standard land use categories (e.g. water, power, communication systems) and, second, production and service elements within a particular land use area-category (e.g. individual buildings in an industrial estate or government center or university complex). In both cases, land use planning will not directly lead to measures that can reinforce, for example, a water distribution network that simultaneously services residential subdivisions, factories, schools, etc., or measures that prioritize among individual structures such as a widely-patronized public market and an adjacent and unmanned market storehouse, to cite another example.

n additional limitation to the use of land use planning for earthquake disaster mitigation, especially in large cities such as Metro-Manila, is the difficulty in or the slow process of changing land use. Often, urban land use cannot be altered according to proposed disaster mitigation measures because changes in the ownership, occupancy, or physical environment of urban lands are difficult to do in the short term. Substantial changes in urban land use usually take place only after decades of conscious and purposeful efforts on the part of the public and private sectors. This requires a relatively stable structure of public administration that is the exception rather than the rule in developing countries. Frequently, more immediate action steps can be taken to mitigate the effects earthquake-related disasters through strategic planning.

 

2. LIFELINE SYSTEMS PLANNING

The effects of the July 16, 1990 earthquake has emphasized the importance of decentralizing and strengthening key utility systems, particularly those concerned with the delivery of water, power, transportation and communication services to large urban centers. In this case, the objective is to minimize the possibility of a total disruption of these services in the event of earthquakes. This can be addressed by a) decentralizing utilities in terms of the location or alignment of their production and distribution elements and by b) strengthening vulnerable components or sections of the systems. In the former, decentralization would help minimize the possibility that damage suffered in one part of the system will paralyze the entire service operation. A process can be initiated so that systems can be gradually decentralized, inputting local geological analyses in order to avoid sites identified as prone to earthquake-related damage including those caused by liquefaction or slope failures. It should be mentioned, however, that decentralization does not necessarily mean deconcentration or a reduction of land use densities. For utility and service networks, decentralization refers to the physical structure of systems that support land use activities which may remain at high density levels.

As far as strengthening vulnerable components of production and distribution systems is concerned, this maybe used as an initial alternative or as a complementary task to decentralization. Here, the spatial layout of a service system is maintained but potentially vulnerable sections, identified through seismic or broader hazard zonification studies, are strengthened to withstand specific earthquake intensities.

The crucial role of transportation networks in earthquake disaster mitigation should be given appropriate attention by urban and regional planners, especially in light of the isolation of many parts of Luzon from major market and supply centers soon after the 1990 earthquake. Urban and regional planners need to incorporate into their planning processes, as an additional criterion for selecting and prioritizing road projects, consideration for projects that may serve as important alternate routes in the event that primary thoroughfares are rendered impassable by future earthquakes.

 

3. BUILDING STOCK MANAGEMENT

A scientific planning approach to earthquake disaster mitigation requires detailed information about an area's building stock. This should include data on the location, type of structure and materials used, floor area, date of construction, renovations and additions, cost or assessed value, density, occupancy, and activities that have taken and are taking place in individual structures. These information would help planners estimate the probabilities and consequences of various earthquake-related damages according to earthquakes of different intensities and serve as a guide in the formulation and prioritization of earthquake disaster mitigation plans.

Building stock inventories are also useful for other purposes that are not directly related to earthquake disaster mitigation. It can be an important input to other development planning efforts--to the fiscal objectives of local governments in relation to building and property tax assessments, to historic preservation efforts, and as a contribution towards the documentation of local culture and tradition.

Building stock inventories arc not easy to make and to update, especially in large cities in the developing world where a large part of the total stock is associated with the informal sector. Many structures, for example, are squatter houses that are of temporary construction, difficult to document in detail and to monitor for future inventories. Further, there is likely to be resistance on the part of resident families to be surveyed for fear that this will lead to unwanted government measures such as additional taxes or relocation.

One specific step that may be taken to institutionalize building stock inventories is to make use of the regular census surveys so that additional, detailed building stock information is gathered regularly. In particular, the ten-year population and housing census conducted by the government may be expanded so that a) additional data on the physical characteristics of structures, especially their specific locations, are acquired, and b) data disaggregation goes down from the level of individual cities or provinces to the barangay or even sub-barangay level.

 

4. METROPOLITANIZATION AND REGIONAL PLANNING

Functional metropolitanization or the interrelated growth and expansion of cities and their adjacent areas should be expected throughout the country and the July 16, 1990 earthquake has served to emphasize the importance of coordinating urban planning and implementation in these areas.

Aside from Metro-Manila, Metro-Cebu, and Metro-Davao, other urban centers of the country have grown to the point that their influence on adjacent municipalities is already difficult to ignore. In Luzon, metropolitan development may be expected to be manifested through the emergence of a Metro-Baguio (or the proposed Metro-BLIST including Baguio City, La Trinidad, Itogon, Sablan, and Tuba), a Metro-Olongapo (Olongapo and Subic), a Metro-Dagupan (Dagupan City, Calasiao, Binmaley, Mangaldan, and San Fabian), a MetroAngeles (Angeles City, San Fernando and Mabalacat), and a Metro-Batangas (Batangas City, San Pascual and Bauan). In the Visayas Islands, a Metro-Iloilo (Ilo-ilo, Pavia); and aMetro-Bacolod (Bacolod, Talisay, Silay) may not be too far off. Finally, in Mindanao, we may expect a MetroZamboanga and a Metro-Cagayan de Oro to emerge.

he virtue of metropolitan planning is that it allows for greater coordination and implementation of earthquake disaster mitigation plans and programs at the same time that urgent measures to improve or provide basic services area also implemented. For example, it allows for greater flexibility in identifying and tapping potable water sources because the planning area extends beyond a single city or municipality, at the same time that decentralization of the water distribution system, following earthquake disaster mitigation objectives, is implemented.

In the field of transportation, to cite another example, circumferential routes may be planned and constructed in many urban centers in order to relieve congestion in or near the traditional central business district as well as to establish or influence the direction of future growth. At the same time, circumferential routes can also play an important role in times of emergency by providing alternate routes to and from various areas of the metropolitan area. Such routes reduces the possibility that parts of the metropolitan areas will be isolated when primary access routes are blocked due to earthquakes or any other disaster. In almost all cases, circumferential routes have to run across various cities and municipalities sot that they are best planned and perhaps even built and maintained under a metropolitan framework.

 

5. HOUSING AND NON-ENGINEERED STRUCTURES

About 90 percent of the building stock in the areas affected by the 1990 earthquake was non-engineered, designed and built by private homeowners, carpenters, and other nonprofessional builders. A large majority of these structures were residential buildings.

Among the residential buildings, reinforced concrete structures performed badly compared to timber-framed houses during the 1990 earthquake. The large proportion of nonengineered reinforced concrete structures in the earthquake-affected areas is indicative of the trend for more and more houses in the Philippines to use concrete and masonry construction materials, instead of traditional native building materials, without the benefit of formal engineering know-how. The trend is a result of a combination of factors which has led to the scarcity of traditional building materials: the increased demand for housing, the reductions in timber and other natural resources due to land conversion and exploitation, and the predominant desire among homeowners for structural permanence, to name several.

It is difficult or unrealistic to expect that the trend towards concrete and masonry construction will not continue, so to increase the ability of non-engineered structures to withstand earthquakes, one must disseminate appropriate information about concrete and masonry technology, design, and construction. The mechanisms for doing this are still unclear, especially considering the complicated principles of reinforced concrete construction relative to timber construction. In the case of the latter, a traditional apprenticeship system has sufficed. It is probably more difficult to institutionalize a similar system for reinforced concrete construction but it may be the only option for the immediate future. As a first step, stricter implementation of housing construction standards through building and local occupancy permits would be welcome. This may be complemented by spreading the liabilities for unexpected structural failures to include local building and inspection officials. On the part of urban planners, geological analyses including hazard mapping and seismic zonification studies need to be incorporated into local land use plans and strategic utility system designs.

 

6. PLANNING EDUCATION

The institution of formal urban and regional planning education in the Philippines as well as in the rest of the world is fairly recent compared to other disciplines. Because of this, and since major earthquakes are relatively infrequent events, the occurrence and effects of earthquakes have yet to be sufficiently integrated into planning education programs. The country's only advanced institution dedicated to urban and regional planning, for example, the School of Urban and Regional Planning of the University of the Philippines, was established only in the 1960s and although there have been about a dozen major earthquakes (magnitude 6.60 or higher) recorded in the archipelago since then, only one or two solicited serious, albeit fleeting, professional attention from urban and regional planners. This is largely due to the lack of expertise among planners in dealing with earthquakes, which is also indicative of the fledgling interaction among planners, geologists, seismic engineers, and other related professionals since the establishments of the School.

The July 16,1990 earthquake should provide impetus for the incorporation of earthquake and other natural disaster mitigation into the field of urban and regional planning. Planners should seek, with even greater initiative than in the past, to learn from the collective experiences of the countries and regions that have experienced earthquakes in the recent decades, and to translate these into relevant policy and program intervention in the Philippines.

Ideally, in the formal planning sector, earthquake disaster mitigation should be integrated into school curricula, training programs, and into public and private reference planning guidelines and manuals. Unfortunately, there is a lack of understanding of how geological events and conditions can be translated into specific courses of action. For example, urban and regional planners have contributed little, by way of what activities and other physical developments should be allowed, to the recent debate on the existence of an active fault line in Metro Manila. Aside from learning from the experiences of other countries, one step that may be taken is to increase interdisciplinary linkages with other fields that are key to earthquake disaster mitigation. This would mean increased interaction with geologists, seismic engineers, and architects. A university-based research institute or committee, encompassing earthquakes as well as other natural disasters, could serve as a venue for such interaction. This is especially relevant in the 1990s and even more so in the next decades for as the country's urban centers continue to grow and expand, as a greater number of people and economic activities concentrate in metropolitan locations, the inevitability of earthquakes remains.

 

7. RIVER AND PLANNING AND MANAGEMENT

While the occurrence of high intensity earthquakes is fairly infrequent, the occurrence of very high intensity earthquakes that can induce liquefaction--those with intensities approaching VIII or higher-is even more infrequent. To be sure, the term "liquefaction" is a new world for many urban and regional planners. It is indicative of both infrequency of the phenomenon and the relative infancy of the field of urban and regional planning. At any rate, the effects of the July 16, 1990 earthquake have provided additional justification for planners to focus greater attention on the rehabilitation and management of urban river systems.

Apart from the obvious need to curb waterborne pollution, appropriate planning and management of city waterways are required because: a) these are the areas which are susceptible to other forms of earthquake-related damage (caused by liquefaction, riverbank failures, etc.), b) rivers serve as emergency routes when other land-based transport routes }re rendered impassable, and c) river banks are sites of large concentrations of residential communities, usually low-income, that are especially vulnerable to earthquakes.

 

NOTES:

1. See also: I. Armillas, J. Petrovski, A. Coburn, D. Lewis, and A. Corpuz. Technical Report on Luzon Earthquake of 16 July 1990, Republic of the Philippines, with recommendation for Reconstruction and Development. Expert Mission to Assist in Reconstruction and Development after the Philippines Earthquake of 16 July 1990 PHI/90/1701, United Nations Centre for Human Settlements (HABITAT), Nairobi, December 1990.
   
2. Ibid.
   
3. Specific information that would be directly relevant to the assessment of the earthquake vulnerabilities of buildings are outlined in: J. Petrovski, Building Damage Classification and Loss Assessment, attachment to 1. Armillas, J. Petrovski, A. Coburn, D. Lewis, and A. Corpuz, 1990.
   
4. A. Corpuz, Dagupan City Urban Planning and Land Use Assessment after the July 16, 1990 Earthquake. Technical Report submitted to the Development Academy of the Philippines, September 1991.
   

5. E. Booth, A. Chandler, P. Wong, A. Coburn. The Luzon, Philippines Earthquake of july 16, 1990: A Field Report by EEFIT London: EEFIT, 1991. See also: National Economic Development Authority, Republic of the Philippines. Reconstruction and Development Program. 1990.
   

6. A vulnerability model and a framework for incorporating seismic risk mitigation concepts into urban and regional planning is presented in: I. Armillas, Integrating Seismic Risk Mitigation Concepts into the Planning Process, attachment to 1. Armillas, J. Petrovski, A. Coburn, D. Lewis and A. Corpuz.