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PRIMER ON THE 06 JULY 2017 MAGNITUDE 6.5 LEYTE EARTHQUAKE 07 July 2017 PDF Print
Friday, 07 July 2017 18:11
What is happening in Leyte?

At 4:03 PM on 06 July 2017, Thursday, a strong earthquake of magnitude 6.5 shook the island of Leyte. The epicenter is located 15.5 km northeast of Ormoc City, Leyte and with a focal depth of 2 km.  The earthquake was generated by the movement of Leyte Segment of the Philippine Fault. Small-magnitude earthquakes followed afterwards, and as of 1:00 PM of 07 July 2017, 297 aftershocks have been recorded by the PHIVOLCS seismic monitoring network.

Based on preliminary intensity reports, the strongest ground shaking was felt at PHIVOLCS Earthquake Intensity Scale (PEIS) VII (Destructive) at Ormoc City and Kananga in Leyte. Furthermore, the municipalities of Jaro and Capoocan in Leyte experienced the ground shaking at PEIS VI (Very Strong), while the municipality of Palo in Leyte, Tacloban City, Cebu City, and Mandaue City felt ground shaking at (PEIS) V (Strong). This earthquake was felt at PEIS IV to I as far as 230 km away (such as Roxas City in Capiz, Iloilo City in Iloilo, La Carlota City in Negros Occidental, and Catarman in Northern Samar) from the epicentral area.  The strong ground shaking near the epicentral area resulted to damages to some buildings, roads and bridges.

 

Moderate magnitude earthquake has affected Leyte in the past!

At least four moderate magnitude earthquakes had affected Leyte Island in the past. On 05 July 1994, a magnitude 6.2 earthquake was generated by the movement of the Philippine Fault. During this event, strong ground shaking was felt in Hinundayan, Hinunangan, San Juan, Anahawan, and St. Bernard in Southern Leyte. On 07 June 1947, a magnitude 6.9 earthquake with the epicenter in Carigara, Leyte affected the entire province. The 27 September 1863 magnitude 6.1 earthquake with epicenter at Kananga, Leyte was felt at PEIS VI in the municipalities of Ormoc, Jaro, and Leyte.  The 07 Febuary 1890 magnitude 6.4 earthquake at Barugo, Leyte was strongly felt at PEIS VIII in Barugo while other towns of Leyte province were shaken at intensities ranging from PEIS VII to V. These earthquakes caused significant damage to buildings and roads. Effects of liquefaction and landslide were also documented in some areas.

From time to time, a series of moderately-sized earthquakes, referred to as seismic swarms, are generated by active faults in the area. Some of the seismic swarm episodes occurred in 2012, 2007, 1998, 1994, and 1991 in Southern Leyte. Magnitude range is between 4.3 to 5.5. These events also caused damages to buildings and some infrastructures.

Why do earthquakes occur in Leyte?

Eastern Visayas, including Leyte, is one of the seismically active areas in the country because of the Philippine Fault and the Philippine Trench, which are the main earthquake generators that can affect the area. In addition, there are other local faults which can be sources of small- to large-magnitude earthquakes.

Can these present earthquakes indicate volcanic activity?

No. There are no active volcanoes in the epicentral area.

What can we expect from the current earthquake activity?

The current seismic trend indicates that the magnitude 6.5 earthquake on 06 July 2017 is the main shock, which caused the strong ground shaking.  The succeeding small-magnitude earthquakes are the aftershocks.  The aftershocks may continue to occur for several days to weeks, some of which may be felt. The probability of an earthquake higher than magnitude 6.5 to occur is low.

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

Landslides, rock falls, and other types of mass movements may occur in mountainous or hilly areas. Liquefaction, manifested by sand boils or lateral spread may affect low-lying, water-logged, sandy areas at the banks of rivers.  Tsunami is not expected from the kind of movement of the Philippine Fault - Leyte segment.  The tsunami threat for Leyte would come from the movement of the Philippine Trench, located east of the province.

What should be done by the affected communities?

People are reminded to be cautious of structures visibly weakened or with signs of damage by the 06 July 2017 Leyte Earthquake, as these may be further damaged by aftershocks. In case of houses and other buildings with visible damage, it is best to contact the Municipal/City Engineering Office for advice.  Engineers from the local government, other agencies and organizations should inspect buildings and other infrastructures to determine their integrity, and recommend appropriate actions to concerned/affected groups or individuals.  Slopes should be checked for tension cracks that may have resulted from the strong ground shaking. Tension cracks may make slopes more susceptible to landslides. These areas should be avoided.

The best course of action is preparedness. In case of another felt earthquake, it is recommended that people protect themselves by doing the "duck, cover and hold".  In homes and offices, heavy furniture should be strapped to the walls, and appliances be secured to prevent them from toppling and causing injuries to persons.

What is the role of PHIVOLCS?

PHIVOLCS operates and maintains a network of 93 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 Leyte are the Palo (Leyte) staff-controlled (manned) seismic station, and the Ormoc City (Leyte), Maasin (Southern Leyte), Catarman (Northern Samar) and Borongan (Eastern Samar) remote-telemetered seismic stations.

Aside from monitoring the occurrences of earthquakes, PHIVOLCS also conducts hazards analyses and assessments, and make this information available to the public.  PHIVOLCS works hand-in-hand with other government agencies in mitigating the damaging effects of earthquakes.

) and Twitter (@phivolcs_dost) accounts for earthquake bulletins, volcano updates, hazard maps, and other information on earthquakes and volcanoes.  Earthquake observations may also be reported to PHIVOLCS at telephone numbers (02) 929-9254 and (02) 426-1468 to 79, local 124 and 125.

 

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