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Uncommon traits of Alaskan quakes.

Uncommon traits of Alaskan quakes

The series of moderate to large earthquakes that shook the Gulf of alska last November and March are causing seismologists to question some of their long-held ideas about the seismic potential along the quake-prone Alaskan subduction zone. this region, where the Pacific plate slides underneath the North American plate, has hosted many large earthquakes, including the 1964 killer that devasted Anchorage and other areas of southern Alaska. But what is strange about the recent quakes is they occurred in the Gulf, solely within the Pacific plate. This stands in contract to normal subduction-zone earthquakes, which strike at the boundary between the two plates, reports Harvard University's Adam Dziewonski. As well, the faults that produced the quakes were not typical subduction-style thrust faults -- ones that have planes dipping away from the horizontal. Instead, the movement was along faults with vertical planes running in a north-south direction.

The recent seismic action occurred several hundred kilometers south of the Yakataga gap -- a quiet section along the subduction zone that seismologists have targeted as the likely site of a large earthquake expected within the next 20 years. However, Dziewonski says the Gulf earthquakes may have released some of the seismic strain building up within the nearby gap, lowering the chances of a large in this area.
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Author:Monastersky, Richard
Publication:Science News
Date:May 28, 1988
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