2012 Samar earthquake

An earthquake off the coast of Samar occurred on August 31, 2012, at 20:47 local time (12:47 UTC) in the Philippines. The populated islands of Visayas were struck by an earthquake of magnitude Mw 7.6.[2] The earthquake has a depth of 45 km (27.9 miles). A tsunami warning was announced within the Pacific area and was later lifted after two hours. The Philippine archipelago is located in the Pacific Ring of Fire, where earthquakes and volcanic activity are common.

2012 Samar earthquake
UTC time2012-08-31 12:47:33
ISC event601667544
USGS-ANSSComCat
Local dateAugust 31, 2012 (2012-08-31)
Local time20:47 PST[1]
MagnitudeMw 7.6[1]
Depth45 km[1]
Epicenter10°50′N 126°43′E[1]
TypeIntraplate earthquake
Areas affectedPhilippines
Max. intensityPEIS – VII (Destructive)[2]
TsunamiYes (highest 20 inches) [3]
Aftershocks298 (as of September 2, 2012)
Casualties1 dead, 1 injured (as of September 1, 2012)[4]

Geology

The Philippine Mobile Belt is between the Eurasia Plate and the Philippine Sea Plate. The Philippine Sea Plate is subducting along the Philippine Trench in this region. At the latitude of the earthquake, the Philippine Sea Plate moves in the WNW direction at a velocity of approximately 100 mm/yr with respect to the Sunda Plate.

This earthquake was an intraplate earthquake greater than 50 kilometers to the east of the boundary of the Philippine Sea Plate. This earthquake was unusual in that it occurred as a result of reverse faulting within the oceanic lithosphere of the Philippine Sea Plate. There have been approximately 40 events of M6 and above over the past 40 years, within 250 km of this earthquake. Most of those earthquakes were the result of normal faulting within the shallower oceanic lithosphere rather than deeper reverse faulting like this event.[5]

Earthquake
Apr 1995
May 1995
Jun 1996
2012
Strong earthquake events near the area were in April 1995 (7.2 Mw), May 1995 (7.1 Mw), June 1996 (7.1 Mw), and the Aug 2012 event (7.6 Mw). See also map below.
The Philippine Trench in the east, and the Philippine Mobile Belt.

After the initial earthquake, the power supply was cut off in affected areas after power lines were damaged. Power plants in Visayas tripped or shut down following the earthquake, although no major damage was sustained in transmission facilities.[6]

A house in the southern city of Cagayan de Oro, Mindanao, was involved in a landslide along with several other homes, killing one of its inhabitants and hospitalizing another.[7]

In General MacArthur, Eastern Samar, 77 homes were damaged. There were also 6 houses damaged in Barangay Casoroy, San Julian.[8] A wall from an old building collapsed in Butuan City.[9]

The NDRRMC reported on Saturday noon that cracks had occurred in some structures such as bridges and roads.[10] The damage was not severe.[11]

Tsunami

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) gave a level three tsunami alert in the Philippines and Other institutes gave a level three tsunami alert in Japan, Indonesia, Taiwan, Palau indicating that the public should be on watch for "unusual waves", but did not call for any evacuation. The Pacific Tsunami Warning Center rapidly issued tsunami warning in the Pacific together with its adjacent islands. However, it was lifted after two hours as no tsunami was recorded. In Japan, the Japan Meteorological Agency issued tsunami warning throughout the coastal areas of the country. The Hong Kong Observatory also issued tsunami warning on Hong Kong on that same time.

About an hour after the quake, sea level readings from gauges in the epicentral region confirmed that a tsunami had been generated.[12] A small 3 cm (1.2 in) wave was recorded at Legazpi in Albay province shortly thereafter, as well as further south near Davao City; slight sea level anomalies were observed in several other locations.[13]

Response

Based on preliminary estimates of the magnitude, specialists noted that a significant tsunami could have been generated. A tsunami warning was issued within 8 minutes after the tremor for coastal regions of the Philippines, Indonesia, Taiwan, Guam, and Japan, as well as for the island nations of Palau, Yap, and Northern Mariana. A tsunami watch was at the time in effect for much of Micronesia, the Solomon Islands, Hawaii, and the Pacific coast of Russia.[14][15] Most of the warnings and watches were quickly cancelled following revisions to the earthquake's intensity, although the warnings for the Philippines, Indonesia and Palau remained in effect.[16]

The tremor caused widespread panic in Eastern Visayas, where many inhabitants exited their homes.[17] At the risk of destructive waves, officials in the Philippines urged remaining residents of eastern coastal areas to evacuate to higher ground.[16]

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See also

References
  1. "Earthquake Bulletin No. 5: 7.6 Samar Earthquake". Philippine Institute of Volcanology and Seismology. August 31, 2012. Retrieved August 31, 2017.
  2. "2012_0831_0540". Retrieved 28 December 2016.
  3. "Most Popular E-mail Newsletter". USA Today. 2012-09-01.
  4. Santos, Matikas. "7.6 quake jolts PH; 1 dead, child hurt". Retrieved 28 December 2016.
  5. "M 7.6 - Philippine Islands region". Retrieved 28 December 2016.
  6. Fujita, Akiko (2012-08-31). "Quake off the Philippines triggers Tsunami Alert". ABC News. Retrieved 2012-08-31.
  7. "At least 1 dead in 7.6 Philippines quake, small tsunami reported, warning canceled". Fox Newsdate=2012-08-31. Associated Press. 2012-08-31. Retrieved 2012-08-31.
  8. News, ABS-CBN. "Quake damages 77 homes in E. Samar town". Retrieved 28 December 2016.
  9. News, ABS-CBN. "Quake causes panic, damage in Visayas, Mindanao". Retrieved 28 December 2016.
  10. "Strong quake, but minimal effects; gov't". The Philippine Star=2012-09-02. Xinhua. Retrieved 2015-06-04.
  11. "Philippine families rebuild amid further quake fears". Business Recorder=2012-09-02. Agence France-Presse. Retrieved 2012-09-02.
  12. Tsunami Bulletin Number 003: 1425Z 31 Aug 2012 (Report). Pacific Tsunami Warning Center. 2012-08-31. Retrieved 2012-08-31.
  13. Tsunami Bulletin Number 004: 1454Z 31 Aug 2012 (Report). Pacific Tsunami Warning Center. 2012-08-31. Retrieved 2012-08-31.
  14. Tsunami Bulletin Number 001: 1255Z 31 Aug 2012 (Report). Pacific Tsunami Warning Center. 2012-08-31. Archived from the original on August 31, 2012. Retrieved 2012-08-31.
  15. Bulletin: Tsunami Message Number 1: 257 AM HST Fri Aug 31 2012 (Report). Pacific Tsunami Warning Center. 2012-08-31. Archived from the original on August 31, 2012. Retrieved 2012-08-31.
  16. Agence France-Presse (2012-08-31). "7.6 quake off Philippines". Bangkok Post. Retrieved 2012-08-31.
  17. Birsel, Robert (2012-08-31). Laurence, Jeremy (ed.). "7.6 earthquake: Tsunami alert for Philippines, Indonesia only". Christian Science Monitor. Retrieved 2012-08-31.
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