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Pacific tsunami greater than 1964's is possible


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POSTED: Tuesday, July 21, 2009

U.S. and British scientists studying mud, sand and soil layers along the coast of Alaska have concluded that the Pacific can expect a tsunami even greater than the one in 1964 that took 122 lives.

“;Our radiocarbon-dated samples suggest that previous earthquakes were 15 percent bigger in terms of the area affected than the 1964 event,”; said lead scientist Ian Shennan, of Durham University in England. “;This historical evidence of widespread, simultaneous plate rupturing within the Alaskan region has significant implications for the tsunami potential of the Gulf of Alaska and the Pacific region as a whole.”;

The 1964 earthquake, the second largest in recorded history with a magnitude of 9.2, caused extensive damage in Alaska and along the West Coast but little in Hawaii.

But evidence of quakes over the past 2,000 years shows two that were even stronger, the scientists said.

Hawaii could take a bigger hit than the West Coast in such a scenario, said Gerard Fryer, a geoscientist with the Pacific Tsunami Warning Center in Ewa Beach. But he said the tsunami probably would be no worse than the one in 1946, when a smaller quake, roughly 8.5 in magnitude, focused wave energy right at Hawaii.

“;A bigger earthquake could cause us some problems, but it would not be as bad as 1946,”; said Fryer, who was not part of the study. “;1946 is sort of the worst case for us. It was exquisitely bad.”;

In Hawaii, 159 people died.

The research team from Durham University, the University of Utah and Plafker Geohazard Consultants carbon-dated peat layers and sediments, and analyzed the distribution of mud, sand and peat within them.

“;Peat layers provide a clear picture of what's happened to the Earth,”; said Shennan in a news announcement by the American Association for the Advancement of Science. “;Our data indicate that two major earthquakes have struck Alaska in the last 1,500 years and our findings show that a bigger earthquake and a more destructive tsunami than the 1964 event are possible in the future.”;

The study, published in the journal Quaternary Science Reviews, looks at a possible tsunami generated by the simultaneous rupture of two sections of the quake zone south of the Aleutians: the 500-mile-long section that produced the 1964 tsunami, and the 155-mile-long Yakataga gap directly to the east.

The result, according to Fryer, would be a quake similar to the one off Chile in 1960, the largest in recorded history at 9.5 magnitude.

“;If you put a Chile-size earthquake up in Alaska, that would give us what these guys are talking about,”; he said. “;That is close to the maximum size an earthquake can be, so we know what the worst is.”;