Update as of 27 July 2022

 

What is happening in northwestern Luzon?

At 08:43 AM Philippine Standard Time (PST) of 27 July 2022 (Wednesday), a major Magnitude (M_w) 7.0 earthquake shook the provinces in northwestern Luzon and adjacent areas including Metro Manila. The earthquake has an epicenter located 17.64°N, 120.63°E - 003 km N 45° W of Tayum (Abra) and a depth of 17 kilometers. As of 3:00 PM,  27 July 2022, 254 aftershocks ranging from M 1.5 to M 4.7 were recorded, 48 of which were plotted, and 11 were felt  (Figure 1).

 

 

Using the PHIVOLCS Earthquake Intensity Scale (PEIS), the preliminary intensity reports* are summarized below.

 

Province	Intensity (PEIS)- Reported
	VII (Destructive)	VI (Very strong)	V (Strong)
Abra	Bucloc, Manabo		Bucay
Cagayan			Peñablanca
Benguet		Baguio City	Almagro, Tagapul-an
Ilocos Sur		Bantay, San Esteban, Sinait, Vigan City	Magsingal, San Juan
Metro Manila			Malabon City, Manila City
Nueva Vizcaya			Bambang
Pangasinan		Dagupan City, Laoac	Alaminos City, Labrador
Tarlac			Concepcion, Tarlac City
Pampanga			Mexico

Province	Intensity (PEIS)- Reported
	IV (Moderately strong)	III (Weak)	II (Slightly felt)	I (Scarcely perceptible)
Bataan	Balanga
Bulacan	Guiguinto, Obando, San Rafael	Bulakan
Kalinga	Tabuk City
Laguna	Famy, Sta. Cruz, Sta. Maria		Santa Rosa City
Metro Manila	Marikina City, Pasig City, Quezon City, Taguig City, Valenzuela City
Nueva Vizcaya	Bayombong, Diadi
Pangasinan	Bautista, Malasiqui	Bolinao
Rizal	San Mateo	Tanay

 

Province	Intensity (PEIS)- Instrumental
	VII (Destructive)	VI (Very strong)	V (Strong)
Benguet			Baguio City
Cagayan			Peñablanca
Ilocos Norte			Laoag City
Ilocos Sur	Vigan City		Sinait
Pangasinan			Dagupan City

 

Province	Intensity (PEIS)- Instrumental
	IV (Moderately strong)	III (Weak)	II (Slightly felt)	I (Scarcely perceptible)
Aurora	Baler
Bulacan		Bulakan, Guiguinto, Malolos City, Plaridel, San Ildefonso	Angat, Doña Remedios, Santa Maria, Trinidad	Marilao
Cagayan	Claveria, Gonzaga
Camarines Norte				Mercedes
Cavite			Tagaytay City	Carmona
Isabela	Ilagan, Santiago City
Kalinga	Tabuk
Metro Manila		Malabon City, Navotas City, Quezon City	Pasig City	Las Piñas City, San Juan City
Nueva Ecija	Cabanatuan City, Palayan City, San Jose
Nueva Vizcaya	Bayombong
Pampanga		Guagua, Magalang
Pangasinan	Basista	Bolinao, Infanta, Sison
Quezon			Gumaca, Infanta, Polillo	Lucban
Province	Intensity (PEIS)- Instrumental
	IV (Moderately strong)	III (Weak)	II (Slightly felt)	I (Scarcely perceptible)
Quirino	Madella
Rizal				Antipolo City, Morong, Tanay, Taytay
Tarlac	Ramos	Tarlac City
Zambales		Iba		Olongapo City, Subic

* Sourced from Earthquake Information No. 2 issued on 27 July 2022 08:43 AM as reported by various affected stakeholders

 

 

Figure 2 provides the simulated earthquake intensity (PEIS) map generated using the DOST-PHIVOLCS Rapid Earthquake Damage Assessment System (REDAS). The intensity map provides predicted intensities for areas without reported intensities.

The 27 July 2022 M7.0 earthquake was felt with a maximum ground shaking intensity of  PEIS VII (Destructive) with some isolated areas experiencing PEIS VIII. At PEIS VII, most people get frightened and run outdoors. People find it difficult to stand on the upper floors. Heavy objects and furniture overturn or topple. Trees are shaken strongly. Big church bells may ring. Old or poorly-built structures suffer  considerable damage. Some well-built structures are slightly damaged. Some cracks may  appear on dikes, fish ponds, road surfaces, or concrete hollow block walls. Liquefaction effects  (e.g. subsidence, sand boils, lateral spreads, etc.) in low-lying areas and landslides in  mountains are observed near the epicenter.

Have major to moderate magnitude earthquakes affected Abra, Ilocos Norte and adjacent provinces in the past? 

At least 40 recorded historical earthquakes were reported from between 1589 and 1985 sourced from Southeast Asia Association of Seismology and Earthquake Engineering  (SEASEE) Report (1985) in Abra, Ilocos Norte and adjacent provinces. Ten of these earthquakes had magnitudes ranging from M3.8 to M5.6, that reported to have affected Abra Province and vicinity. Two major earthquake events with significant magnitudes are listed below:

• September 1862 -M6.2 earthquake with epicenter in Ilocos Norte occurred which resulted in some damage to buildings in various towns, especially in Piddig, Ilocos Norte. Abra experienced strong ground shaking lasting about a minute. There were four aftershocks of equal strength but of shorter duration. But no damage was reported.
• 12 September 1877- The largest earthquake event (M5.6) with epicenter in Abra Province occurred with Bangued, Abra reported to have experienced some damages to tile roofs.

Why do earthquakes occur in northwestern Luzon?

Northwestern Luzon is one of the seismically active regions in the country because of the presence of  active faults that include the northern segments of the Philippine Fault, Abra River Fault, West Ilocos Fault System, and Naglibacan Fault. There are other nearby local faults, some of which may now be covered by recent deposits, and offshore active faults that are potential sources of minor to strong earthquakes. 

Can this earthquake indicate volcanic activity?

No. The nearest active volcano is the Cagua Volcano, which is approximately 170 kilometers northeast from the epicenter. More importantly, this earthquake event is tectonic in origin. 

What can we expect from the current earthquake activity?

Minor to moderate aftershocks are expected to occur in the epicentral area but occurrences  of strong aftershocks cannot be discounted. These may continue for several days to weeks,  some of which may be felt.

Aside from strong ground shaking, what other seismic hazards are life-threatening?

Landslides, rock falls, and other types of mass movements may occur on mountainous or hilly  areas. Liquefaction, manifested by subsidence, sand boils or lateral spreads may affect low lying, water-saturated, and sandy areas near riverbanks and shorelines. In particular, coastal  areas are vulnerable to inundation of seawater due to the combination of liquefaction-induced  subsidence and changes in sea level during high tide.

Can this recent earthquake event trigger a destructive tsunami?

No. The 27 July 2022 M7.0 event happened onshore. Hence, no destructive  tsunami waves were generated because there was no significant vertical displacement of the seafloor. More often, tsunamis are produced by earthquakes with significant vertical movements and from earthquakes generated by active trenches. However, localized sea-level  disturbances may be observed as a result of ground shaking or submarine landslides. 

What should be done by the affected communities?

People are reminded to be cautious of structures visibly weakened, having signs of damage or are partially collapsed by the 27 July 2022 event. The expected aftershocks may also  cause further damage to already weakened structures. In the case of houses and other  buildings with visible damage, it is best to contact the concerned Municipal/City Engineering Office for advice and inspection. Civil engineers from the local government, other agencies and organizations are strongly enjoined to inspect buildings and infrastructure to determine their integrity and recommend appropriate actions to the affected population. Structurally compromised buildings should not be reoccupied unless certified as safe by structural engineers.

Slopes should be checked for tension/incipient cracks that may have resulted from the strong  ground shaking. Tension cracks may render slopes more susceptible to landslides. Such areas should be avoided.

The best course of action is preparedness. In homes and offices, heavy furniture should be  strapped to the walls, hanging objects securely fastened, and appliances secured to prevent  these from toppling and causing injuries to persons. In case of another strongly felt  earthquake, it is recommended that people protect themselves by doing the “drop, cover and  hold.”

Immediate life safety is the priority when evacuation after an earthquake is necessary. It is  important for the public to understand that an earthquake evacuation takes priority over a  COVID-19 Stay-at-Home order. It is also important that risks of COVID-19 spread among the public in evacuation are managed. At all times, people affected by the earthquake are  also strongly advised to wear face masks and to strictly observe physical distancing before, during, and after evacuation.

During earthquake events, rumors and unverified information that may cause panic are easily spread. Please avoid sharing messages from unconfirmed and unreliable sources. 

What is the role of DOST-PHIVOLCS?

DOST-PHIVOLCS operates and maintains a network of 115 seismic stations spread across  the Philippines. Data from the seismic stations are used to determine the location, magnitude  and other characteristics of the earthquakes generated.

The closest seismic stations to Abra are the staff-controlled seismic stations in Pasuquin in Ilocos Norte, Baguio City in Benguet, Sinait in Ilocos Sur, Penablanca in Cagayan; and satellite-telemetered seismic stations Dolores in Abra, Santa in Ilocos Sur, Sagada Mountain Province, Conner in Apayao, Tabuk City in Kalinga, Pamplona and Gonzaga  in Cagayan, Aguinaldo in Ifugao, Bolinao and San Manuel, Pangasinan, Cabarroguis, Quirino, Cauayan and Palanan in Isabela, Aritao in Nueva Vizcaya, Casiguran in Aurora.

Aside from monitoring earthquakes, DOST-PHIVOLCS also provides other services such as  hazards analyses and assessments. DOST-PHIVOLCS works hand-in-hand with other  government agencies in mitigating the damaging effects of earthquakes. Furthermore, DOST-PHIVOLCS is immediately deploying personnel from the Main Office to assess impacts, hazards, and conduct information dissemination campaigns to allay the fears  of the public. 

Please visit our website at www.phivolcs.dost.gov.ph, and our Facebook (/PHIVOLCS) and  Twitter (@phivolcs_dost) accounts for earthquake information, volcano updates, hazard  maps, and other information on earthquakes and volcanoes. Earthquake observations may  also be reported to DOST-PHIVOLCS at telephone numbers (02) 8929-9254 and (02) 8426- 1468 to 79, local 307 and 308.

 

*Minor earthquakes: 3 to 3.9; Light earthquakes: 4 to 4.9; Moderate earthquakes: 5 to 5.9; Strong earthquakes: 6 to 6.9; Major earthquakes: 7 to 7.9; Great earthquakes: 8.0 and above.

 

Download PDF copy: https://bit.ly/2022M7NWLuzonEQ-Primer