Phivolcs has released a primer on the deadly Philippines earthquake. Check it out below:
What happened at Bohol?
At 8:12 AM on 15 October 2013, Tuesday, a destructive earthquake of
magnitude 7.2 shook the island of Bohol and nearby provinces.
Smaller-magnitude earthquakes followed afterwards, and as of 1:00 pm, 16
October 2013, 885 earthquakes have been recorded by the PHIVOLCS
seismic monitoring network. At least 15 events were reportedly felt in
the epicentral area. The main shock and succeeding aftershocks were
located in the vicinity of Bohol. These recorded events were shallow,
with a depth of at most 32 kilometers. Based on spatial distribution of
succeeding events and characteristics of the earthquake, the event is
tectonic in origin.
Based on preliminary intensity reports, the strongest ground shaking
at PEIS VII was felt at Tagbilaran City and several cities in the
province of Cebu. Neighboring island provinces of Cebu, Negros
Occidental, Negros Oriental, Camiguin, Panay, Leyte, and several areas
in northeastern Mindanao felt the earthquake at varying intensities of
PEIS I-VI.
Moderate-magnitude (M5 to 6.9) earthquakes have also affected Bohol Island in the past!
On 08 February 1990, a magnitude 6.8 earthquake occurred at Bohol
generated by an offshore reverse fault east of the island. Sixteen
municipalities felt the strongest intensity of ground shaking at PEIS
VIII. There were reports of severe property damages, numerous
casualties, hundreds injured, and several thousands homeless. The towns
of Jagna, Duero, Guindulman, Garcia Hernandez, and Valencia experienced
tsunami inundation.
Why do earthquakes occur in Bohol?
Bohol Island is one of the seismically active areas in the country.
Instrumental monitoring of earthquakes for the past century has detected
many small to moderate-magnitude earthquakes in Bohol Island. There is
at least one known earthquake generator on the island, the East Bohol
Fault. In addition, there are other local faults which can be sources of
small to large magnitude earthquakes. Earthquakes can also occur
offshore or undersea because of local offshore faults near the island or
trenches in the vicinity of the region.
Can these present earthquakes indicate volcanic activity?
No. There are no volcanoes in Bohol Island.
What can we expect from the current earthquake activity?
The current seismic trend indicates that the magnitude 7.2 earthquake
on 15 October 2013 is the main shock, and the succeeding small
magnitude earthquakes are the aftershocks. Aftershocks are expected,
some of which will be felt. These may continue for weeks to months, but
diminishing in number and strength as time passes. In this case, a
higher magnitude earthquake related to this event is no longer expected
to occur.
What can we expect after a large-magnitude/high-intensity earthquake like this?
People are reminded to be cautious of structures visibly weakened or
with signs of damage by the 15 October 2013 earthquake, as these may be
further damaged by succeeding earthquakes. Strong ground shaking may
cause extensive damage to or even the collapse of houses, buildings,
bridges, and other infrastructures. Collapsed structures usually account
for most of the casualties during a strong earthquake. Falling objects
may also cause injuries.
What should we do?
Report from the field mentioned several building, houses and other
infrastructures that sustained minor to major damages. In case of houses
with visible damage, it is best to contact the Municipal Engineering
Office for advice. Engineers from the municipal government and other
authorities should inspect buildings and other infrastructures to
determine their integrity and recommend appropriate action to concerned
affected groups or individuals. Check for tension cracks on the ground
that may have resulted by the strong ground shaking. These areas can
initiate landslides during intense rainfall.
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 injury to persons.
Aside from strong ground shaking, what other seismic hazards are life-threatening?
Landslides, rock falls, and other types of mass movement may occur in
mountainous or hilly areas. Liquefaction, manifested by sandboils or
lateral spreading may affect low-lying, water-saturated, sandy areas
near the coast or at the banks of rivers. In general, since the
destructive earthquake occurred inland, no tsunami was generated.
What is the role of PHIVOLCS?
PHIVOLCS operates and maintains a network of 69 seismic stations
spread across the Philippines. Twenty five of these – the manned seismic
stations of Tagbilaran City, Palo, Leyte, Lapu-Lapu City, Camiguin, San
Jose De Buenavista, Roxas City, Capiz, Kalibo, Aklan, Sibulan, Negros
Oriental, Surigao City, Cagayan de Oro City and Dipolog City as well as
unmanned stations of Maasin, So. Leyte, Ormoc City, Butuan City,
Borongan, Eastern Samar, Guimaras and Ipil are located in or around
Bohol. Data from the seismic stations are used to determine the
location, magnitude and other characteristics of the earthquakes
generated.
Aside from monitoring the occurrences of earthquakes, PHIVOLCS also
conducts hazards analyses and assessments, and make the information
available to the public.
PHIVOLCS works hand-in-hand with other government agencies in
mitigating the damaging effects of earthquakes. Please visit our website
at http://www.phivolcs.dost.gov.ph
for earthquake information, volcano updates, and education materials 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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Philippines Earthquake: Phivolcs Releases Primer On The Magnitude 7.2 Bohol Quake
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