Powerful quake off Philippines triggers small tsunami

August 31st, 2012 - 8:33 pm ICT by BNO News  

GUIUAN, PHILIPPINES (BNO NEWS) — A powerful earthquake struck off the eastern coast of the Philippines on Friday evening, prompting a tsunami warning for several countries, seismologists and officials said. A small tsunami was generated, but it was not immediately known if the quake caused damage or casualties.

The 7.7-magnitude earthquake at 8:47 p.m. local time (1247 GMT) was centered about 112 kilometers (69 miles) east of Guiuan, a municipality in the province of Eastern Samar in the Philippines. It struck about 10 kilometers (6.2 miles) deep, making it a shallow earthquake, according to the Philippine Institute of Volcanology and Seismology (PHIVOLCS).

PHIVOLCS issued a level 3 tsunami alert for coastal areas in several provinces, warning residents of high tsunami waves and urging them to move to higher ground. The evacuation of coastal areas was ordered in Northern Samar, Eastern Samar, Leyte, Southern Leyte, Surigao del Norte, and Surigao del Sur.

“People in threatened coastal areas are strongly advised to immediately evacuate to higher grounds,” PHIVOLCS said in a bulletin. “Coastal areas in the [named] provinces are expected to be affected by high tsunami waves. Boats at sea are advised to stay in the deeper parts of the open seas until the threat has passed. If there is sufficient time, boats in harbors and enclosed bays are advised to go to the deeper parts of the open seas until the threat has passed.”

Only small tsunami waves were recorded about two hours after the earthquake struck, but a tsunami warning remains in effect for the Philippines, Indonesia, and the Pacific island nation of Palau. Tsunami warnings earlier issued for Yap, Taiwan, Japan, Guam, the Northern Mariana Islands, and Papua New Guinea have since been canceled.

“Sea level readings confirm that a tsunami was generated. This tsunami may have been destructive along coastlines of the region near the earthquake epicenter,” the Pacific Tsunami Warning Center said in a bulletin. It said it recorded minor tsunami waves of about 3 centimeters (1.1 inch) in two locations, but tsunamis normally grow in size near shallow waters.

“When no major waves are observed for two hours after the estimated time of arrival or damaging waves have not occurred for at least two hours then local authorities can assume the threat is passed,” the center said. “Danger to boats and coastal structures can continue for several hours due to rapid currents.”

A tsunami watch was initially also issued for other islands and countries in the region, including Chuuk, the Japanese coral atoll Marcus Island, Kosrae, Pohnpei, the Marshall Islands, Wake Island, the Solomon Islands, Russia, Nauru and the U.S. state of Hawaii. They were later canceled based on new information from seismologists.

“Based on all available data there is no destructive tsunami threat to the state of Hawaii. Therefore the tsunami watch for Hawaii is canceled,” the Pacific Tsunami Warning Center said in a message to the state’s Civil Defense. “However, some coastal areas in Hawaii could experience small non-destructive sea level changes and strong or unusual currents lasting up to several hours.”

The United States Geological Survey (USGS) initially measured the strength of the earthquake at 7.9, but the magnitude was later revised down to 7.6. The agency estimated the depth of the earthquake to be approximately 39.9 kilometers (21.7 miles), making it a shallow earthquake.

USGS computer models estimated some 117,000 people living in coastal areas near the epicenter may have experienced strong shaking, which could potentially result in light to moderate damage. More than 18.5 million people may have felt light to moderate tremors, the agency said.

Philippines President Benigno Aquino III instructed officials to ensure that emergency evacuations in the affected areas be peaceful and orderly, his spokesperson said in a statement. Social Welfare and Development Secretary Dinky Soliman also said its offices in the region are ready to deliver food packages if needed.

The Philippines is on the so-called ‘Pacific Ring of Fire’, an arc of fault lines circling the Pacific Basin which is prone to frequent and large earthquakes. Volcanic eruptions also occur frequently in the region.

In July 1990, a powerful 7.8-magnitude earthquake struck the densely populated island of Luzon, killing at least 2,412 people and injuring thousands more. It was one of the most deadliest earthquakes in the Philippines in recent history.

Only more deadly was an enormous 8.1-magnitude earthquake in August 1976 which shook Mindanao island and had its epicenter in the Moro Gulf. It caused a destructive tsunami in the Celebes Sea, causing devastation in settlements along the coast of the Moro Gulf on Mindanao island and on the nearby Sulu Islands.

The 1976 earthquake was felt on all of the central islands of the Philippines Archipelago and in the southern part of Luzon. As a result of the earthquake and tsunami, more than 8,000 people were killed or left missing, 10,000 were injured, and 90,000 were left homeless.

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