Three-dimensional P and S wave velocity structure beneath Central Japan

Abstract

Three-dimensional P and S wave velocity structure beneath Central Japan is determined by the seismic wave travel time tomography. Then, we use many data observed by explosion seismic observations, temporary observations in the sea area and so on as well as those by routine observations for natural earthquakes. Results obtained in this study are as follows. The high velocity subducting Philippine Sea plate is revealed. The Philippine Sea plate subducts at a little bit high angle at first, then at a low angle and finally at a high angle. The Philippine Sea plate separates at about 136.5°E, 35.0°N. The obtained Vp/Vs result shows that seismic coupling in northwest neighborhood of the locked area of impending Tokai earthquake is weak. An aseismic Philippine Sea plate is detected at 137.5°E, from 35.6°N to 35.8°N and from 100km to 200 km depth.