AIR Analyzes Samoa Quake/Tsunami

October 1, 2009

According to catastrophe risk modeling firm AIR Worldwide, an earthquake-triggered tsunami flattened villages, submerged tourist resorts and killed more than 100 people in Samoa, American Samoa and Tonga yesterday morning. Samoa was hardest hit; not a building was left standing in the coastal Samoan village of Sau Sau Beach Fale.

The tsunami, “so powerful that it twisted concrete beams and cars, was generated by an earthquake that struck about 195 km (125 mi) south of the Samoan capital of Apia at 17:48 UTC. The U.S. Geological Survey (USGS) issued a preliminary magnitude estimate of 8.0 for the event,” said AIR.

“Depth is estimated at 18 km (112 miles). Aftershocks generated tsunami waves up to six meters (19 feet) high. According to the superintendent of the National Park of American Samoa, tsunami water flowed inland up to 100 meters (328 feet) before receding. All tsunami warnings for Samoa were lifted by yesterday afternoon, however.

“Local officials reported that the damage to villagers’ homes was greatest in Upolu—a rural Samoan island where houses are constructed of light materials.

“Pago Pago, the largest city in American Samoa—which lies to the southeast of Samoa Island—also sustained heavy damage. In addition to those killed, dozens remain missing throughout this cluster of South Pacific islands.”

Dr. Bingming Shen-Tu, principal scientist at AIR Worldwide, explained that the “earthquake occurred on the northern end of the Kermadec-Tonga Subduction Zone, where the Pacific Plate subducts under the Australian Plate at a rate of 8-9 centimeters per year.

“The Kermadec-Tonga Subduction Zone is one of the most active earthquake regions in the world; there have been around 40 quakes equal to or exceeding M 7.5 along this plate boundary since 1900. A magnitude 8.1 earthquake that occurred in the region in 1995 was located just 150 kilometers west of yesterday’s event. The focal mechanism of the quake yesterday suggests a normal fault rupture on or near the outer rise of the subducting Pacific Plate.”

Source: AIR Worldwide –

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