Upper Mantle Velocity Structure Estimated From Ps-Converted Wave Beneath the North-Eastern Japan Arc |
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| Authors: | Toru Matsuzawa Norihito Umino Akira Hasegawa Akio Takagi |
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| Institution: | Observation Centre for Earthquake Prediction, Faculty of Science, Tohoku University, Sendai 980, Japan. |
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| Abstract: | Summary. The upper boundary of the descending oceanic plate is located by using PS -waves (converted from P to S at the boundary) in the Tohoku District, the north-eastern part of Honshu, Japan. the observed PS-P time data are well explained by a two-layered oceanic plate model composed of a thin low-velocity upper layer whose thickness is less than 10 km and a thick high-velocity lower layer; the upper and lower layers respectively have 6 per cent lower and 6 per cent higher velocity than the overriding mantle. the estimated location of the upper boundary is just above the upper seismic plane of the double-planed deep seismic zone. This result indicates that events in the upper seismic plane, at least in the depth range from 60 to 150 km, occur within the thin low-velocity layer on the surface of the oceanic plate. |
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| Keywords: | upper mantle structure converted wave low-velocity layer subduction zone |
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