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PRIMER ON THE 06 JULY 2017 MAGNITUDE 6.5 LEYTE EARTHQUAKE 07 July 2017
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.

 

[Download Primer here]

 
Philippine Fault Article: Tsutsumi, H. and Perez, J.S., Large-scale active fault map of the Philippine fault based on aerial photograph interpretation
Friday, 07 July 2017 00:43

Abstract

The Philippine fault is a ~1250-km-long, left-lateral strike-slip fault extending NNW parallel to the Philippine archipelago. This fault has been very active in the past 200 years with several destructive earthquakes accompanied by surface rupture. However, there was no large-scale map of the Philippine fault, which is essential for mitigating seismic hazard from future earthquakes. We mapped the surface trace of the Philippine fault on 1:50000-scale topographic maps based mainly on interpretation of ~1:30000-scale aerial photographs. We then compiled these fault trace data on a Geographic Information System to produce the first digital active fault map of the Philippine fault. These 1:50000-scale active fault maps are available from the website of Philippine Institute of Volcanology and Seismology (PHIVOLCS). These maps reveal that there are notable along-strike variations in fault trace geometry and magnitudes of historical seismicity of the Philippine fault. The Philippine fault in central Luzon and Mindanao Islands are well segmented and produced large (M≥7) earthquakes. In contrast, the fault in Masbate and Leyte Islands are more continuous and produced only moderate earthquakes in the past 400 years. There are geomorphic and geodetic evidence of aseismic creeping on the Philippine fault in northern and central Leyte. These observations suggest that the Philippine fault may be comparable to the San Andreas fault in that both of the faults are composed of locked, transition and creeping segments as previously suggested.

Full paper: 

Tsutsumi, H. and Perez, J.S., 2013. Large-scaleactive fault map of the Philippine fault based on aerial photograph and interpretation. Active Fault Research, 39, 29-37.

 
Geologist Jeffrey Perez lauded as an Outstanding Young Scientist
Thursday, 06 July 2017 15:36


Jeffrey Perez, Supervising Science Research Specialist of the Department of Science and Technology-Philippine Institute of Volcanology and Seismology (DOST-PHIVOLCS), is hailed as one of the Outstanding Young Scientists by the National Academy of Science and Technology (NAST) for his contributions in the field of geology.

NAST, the highest recognition and advisory body to the government and science community on matters related to science and technology, has recognized Perez for his research findings that provided better understanding of the fault distribution, segmentation, earthquake generation potential, and history of surface-rupturing earthquakes along the different segments of the Philippine fault in eastern Mindanao. He led the active faults and paleoseismic studies along the Philippine fault, and was also part of the team that mapped and conducted paleoseismic studies along the Valley Fault System that traverses Greater Metro Manila Area and other active faults in the Philippines.

Their work has updated the active faults map of the Philippines, which is extensively used in seismic hazard assessment by different stakeholders for land-use and disaster risk reduction mitigation plans. He also effectively communicates geohazard information and disaster risk reduction researches to various stakeholders through engaging lectures and seminars for communities to be pro-active in earthquake and tsunami preparedness.

In addition, Perez received various awards such as the 2015 DOST International Publication Award, 2016, 2015 and 2011 PHIVOLCS Research Publication Award and 2007 PHIVOLCS Model Employee (Technical) Award.

The Outstanding Young Scientist Award will be presented to Jeffrey Perez on July 11, 2017 at World Trade Center, Pasay City and on July 13, 2017 during the National Academy of Science and Technology (NAST) - Annual Scientific Meeting on at Manila Hotel.

 
PHIVOLCS EMPLOYEES PERFORM THE DUCK, COVER, AND HOLD
Thursday, 29 June 2017 18:41

At the sound of the alarm, employees of the Department of Science and Technology - Philippine Institute of Volcanology and Seismology (DOST-PHIVOLCS) performed the Duck, Cover, and Hold technique and evacuated the building as they participate in the 2nd quarter Nationwide Simultaneous Earthquake Drill (NSED).

NSED is a quarterly activity organized by the Office of Civil Defense (OCD) that seeks to heighten public awareness and to educate the public on the importance of preparedness against earthquake hazards.

The 2nd quarter NSED ceremonial venue was held in Davao City at Bolton Street along University of Mindanao on June 29, 2017, Thursday at 2:00 PM. DOST Usec. Renato Solidum, Department of National Defense (DND) Usec. Ricardo Jalad, and Davao City Administrator Zulieka Lopez led the ceremonial pressing of the button to indicate the start of the earthquake drill. The drill in Davao City simulated a Magnitude 7.0 earthquake generated by the Central Davao Fault Zone (CDFZ) with the Intensity of PHIVOLCS Earthquake Intensity Scale (PEIS) VIII [Very Destructive]. Barangay residents, students, and owners of business establishments participated in the community-based drill. Different scenarios were performed to showcase response during a strong destructive earthquake.

As the agency mandated to monitor and study earthquakes, DOST-PHIVOLCS pushes for the continued promotion of earthquake awareness and preparedness since it introduced the conduct of earthquake drills in schools way back 2002.

Philippines is a seismically active country with approximately 90 destructive earthquakes and 40 tsunamis recorded in the past 400 years. Strong earthquakes may result to earthquake hazards such as ground shaking, ground rupture, liquefaction, tsunamis, and earthquake-induced landslide. Awareness and preparedness will increase our chances against natural hazards and disasters.

 
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