High resolution receiver function imaging of the seismic velocity discontinuities in the crust and the uppermost mantle beneath southwest Japan

Clear images of the seismic velocity discontinuities in the crust and the uppermost mantle beneath southwest Japan have been obtained with Receiver Function (RF) analyses of teleseismic waveforms observed at extraordinary dense short-period and broadband stations. For imaging, we construct several 2-D profiles of depth-transformed RFs to delineate the fine crustal structure and the 3-D configuration of the Philippine Sea plate (PHS). The Moho is clearly seen and locally depressed just beneath the Chugoku Mountains. The Conrad, the velocity discontinuity within the crust, in the northern Kinki region is recognized and depressed just beneath the Chugoku Mountains as well as the Moho. RF analyses also clearly elucidate the largely contorted configuration of the PHS including aseismic portions. The PHS subducts aseismically under the western Chugoku region with a high dip angle of 35 degrees at least to a depth of 65 km. In the western Kii Peninsula, it descends steeply to a depth of 90 km with some curvature, while it subducts with a low dip of 20 degrees to a depth of 60 km from the eastern Kii Peninsula to the Lake Biwa.