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 subduction zone, large-scaled narrow region in the earth's crust where, according to plate tectonics, masses of the spreading oceanic lithosphere bend downward into the earth along the leading edges of converging lithospheric plates where it slowly melts at about 400 . this region, where the Pacific plate slides underneath the North American plate The North American Plate is a tectonic plate covering most of North America, extending eastward to the Mid-Atlantic Ridge and westward to the Cherskiy Range in East Siberia. , has hosted many large earthquakes, including the 1964 killer that devasted Anchorage Anchorage (ăng`kərĭj), city (1990 pop. 226,338), Anchorage census div., S central Alaska, a port at the head of Cook Inlet; inc. 1920. 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 Adam Dziewoński (* 1936, in Ukraine, formerly Poland) is a Polish-American geophysicist who has made seminal contributions to the determination of the large-scale structure of the Earth's interior and the nature of earthquakes using seismological methods. He is the Frank B. . 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 Noun 1. north-south direction - in a direction parallel with lines of longitude direction, way - a line leading to a place or point; "he looked the other direction"; "didn't know the way home" . 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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