Pre-seismic crustal deformation caused by an underthrusting oceanic plate,in eastern Hokkaido,Japan |
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| Authors: | Kunihiko Shimazaki |
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| Institution: | Earthquake Research Institute The University of Tokyo, Tokyo Japan |
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| Abstract: | Eastern Hokkaido is being considered as one of the prime candidates for a future great earthquake in Japan. Geodetic work and seismological data suggest that the continental plate is being compressed and dragged down into the asthenosphere by the underthrusting Pacific plate.A quantitative examination of this idea was carried out by an application of the finite-element method to a static-field problem of crustal deformation. The effect of heterogeneous medium with Poisson's ratio differing from 0.25 is significant. An inverse problem was solved by applying a quadratic programming method to the observed vertical displacement.A model, which assumes a nearly uniform tangential displacement along the interface of the oceanic and continental lithospheres down to a depth of 100 km, explains a gravity-change as well as the general features of crustal deformation observed in eastern Hokkaido. The displacement rate is estimated to be 2.7 cm/year. It indicates that a rebound of the continental lithosphere now brings about a thrust-type earthquake whose reverse slip is comparable to that estimated for great shallow earthquakes along the Kuril trench. A possibility of aseismic rebound is suggested at the lower part of the interface. |
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