The cause of the east–west contraction of Northeast Japan

Abstract

(2017) The cause of the east-west contraction of Northeast Japan. Bull. Geol. Surv. Japan, vol. 68 (4), p. 155-161, 5 figs. Abstract: Northeast (NE) Japan, where the Pacific Plate is subducted to the west, frequently suffers large earthquakes not only along the Japan Trench but also along the Japan Sea side. Those occurred in the former area (subduction-zone earthquake) such as the 2011 off the Pacific coast of Tohoku Earthquake can easily be understood as a releasing process of accumulated stress along the boundary between the subducting Pacific Plate and the overlying plate. On the contrary, those in the latter area (inland earthquake), which occur at relatively shallow depth (<20 km), cannot be explained by such a simple dislocation model. Here I show, the cause of such inland earthquakes can be identified by considering the plate kinematics around the Japanese Islands on the basis of three dimensions, not conventional two dimensions, and the cause of the present E-W contractive tectonics of NE Japan is not the Pacific Plate motion itself but the northwestward-moving Philippine Sea Plate.