An earthquake off the coast of Samar occurred on August 31, 2012, at 20:47 local time (12:47 UTC) in the

Philippines The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...

. The populated islands of

Visayas The Visayas ( ), or the Visayan Islands (Bisayan languages, Visayan: ''Kabisay-an'', ; Filipino language, Filipino: ''Kabisayaan'' ), are one of the three Island groups of the Philippines, principal geographical divisions of the Philippines, a ...

were struck by an earthquake of magnitude 7.6. The earthquake occurred at a depth of 45 km (27.9 miles). A

tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...

warning was announced within the Pacific area and was lifted after two hours. The Philippine archipelago is located in the Pacific

Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a tectonic belt of volcanoes and earthquakes. It is about long and up to about wide, and surrounds most of the Pa ...

, where earthquakes and volcanic activity are common.

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 event was an

intraplate earthquake An intraplate earthquake occurs in the ''interior'' of a Plate tectonics, tectonic plate, in contrast to an interplate earthquake on the ''boundary'' of a tectonic plate. They are relatively rare compared to the more familiar interplate earthqu ...

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 A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...

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.

Earthquake

After the initial earthquake, power supply was cut off in the 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. A house in the southern city of

Cagayan de Oro Cagayan de Oro (abbreviated CDO and officially the City of Cagayan de Oro; ; Bukid language, Binukid: ''Ciudad ta Cagayan de Oro''; ; ) is a Cities of the Philippines#Legal classification, highly urbanized city in the Regions of the Philippi ...

Mindanao Mindanao ( ) is the List of islands of the Philippines, second-largest island in the Philippines, after Luzon, and List of islands by population, seventh-most populous island in the world. Located in the southern region of the archipelago, the ...

, was involved in a landslide along with several other homes, killing one of its inhabitants and hospitalizing another. In General MacArthur, Eastern Samar, 77 homes were damaged. An additional six houses were damaged in Barangay Casoroy, San Julian. A wall from an old building collapsed in Butuan. The National Disaster Risk Reduction and Management Council (NDRRMC) reported on Saturday noon that cracks had occurred in some structures such as bridges and roads. The damage was not severe.

Intensity

Tsunami

PHIVOLCS gave a level three

alert in the Philippines and other institutes gave a level three

alert in

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...

Palau Palau, officially the Republic of Palau, is an island country in the Micronesia subregion of Oceania in the western Pacific Ocean. The Republic of Palau consists of approximately 340 islands and is the western part of the Caroline Islands ...

indicating that the public should be on the watch for "unusual waves", but did not call for any evacuation. The Pacific Tsunami Warning Center rapidly issued tsunami warnings 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 The Japan Meteorological Agency (JMA; ''気象庁, Kishō-chō'') is a division of the Ministry of Land, Infrastructure, Transport and Tourism dedicated to the Scientific, scientific observation and research of natural phenomena. Headquartered ...

issued tsunami warnings throughout the coastal areas of the country. The Hong Kong Observatory also issued a tsunami warning on Hong Kong at that same time. About an hour after the quake, sea level readings from gauges in the epicentral region confirmed a tsunami was generated. 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 Davao City, officially the City of Davao, is a City of the Philippines#Legal classification, highly urbanized city in the Davao Region, Philippines. The city has a total land area of , making it the List of Philippine cities and municipalities ...

; slight sea level anomalies were observed in several other locations.

Response

Based on preliminary estimates of the magnitude, specialists noted that a significant

could have been generated. A tsunami warning was issued within eight minutes after the tremor for coastal regions of the Philippines,

Guam Guam ( ; ) is an island that is an Territories of the United States, organized, unincorporated territory of the United States in the Micronesia subregion of the western Pacific Ocean. Guam's capital is Hagåtña, Guam, Hagåtña, and the most ...

, and

, as well as for the island nations of

, Yap, and Northern Mariana. A tsunami watch was at the time in effect for much of

Micronesia Micronesia (, ) is a subregion of Oceania, consisting of approximately 2,000 small islands in the Northwestern Pacific Ocean. It has a close shared cultural history with three other island regions: Maritime Southeast Asia to the west, Poly ...

, the

Solomon Islands Solomon Islands, also known simply as the Solomons,John Prados, ''Islands of Destiny'', Dutton Caliber, 2012, p,20 and passim is an island country consisting of six major islands and over 1000 smaller islands in Melanesia, part of Oceania, t ...

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

, and the Pacific coast of

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

. Most of the warnings and watches were quickly cancelled following revisions of the earthquake's magnitude, although the warnings for the Philippines, Indonesia and Palau remained in effect. The tremor caused widespread panic in Eastern Visayas, where many inhabitants exited their homes. At the risk of destructive waves, officials in the Philippines urged remaining residents of eastern coastal areas to evacuate to higher ground.

References

External links

* {{Earthquakes in the Philippines Samar earthquake 2012 disasters in the Philippines Earthquakes in the Philippines History of Eastern Samar 2012 tsunamis August 2012 in the Philippines