Tectonic landform and geological structure in the Toyama Trough, southeast margin of Japan Sea

Abstract

Hydrographic Department, Japan Maritime Safety Agency conducted multichannel seismic reflection and refraction survey and Sea Beam bathymetric survey in the Toyama Trough extending northward in the southeastern margin of the Japan Sea. The purpose of the survey is to reveal the geological structure and tectonic landform of the Toyama Trough and to examine the hypothesis that the Toyama Trough is subduction zone.
Seismic profiles across the Toyama Trough do not support the presence of distinct subduction zone along the trough because the basement of the trough is not traceable beneath the Sado Ridge. This suggests that the Toyama Trough is different in geological feature from typical subduction zone such as the Japan Trench or the Nankai Trough, where subducting oceanic basement is clearly traceable beneath the overriding plate in seismic profiles. Further, seismic profiles show that the sedimentary layers thicken to the east in some places and to the west in the other places. These features indicate that convergent plate boundary is not present, or only extremely incipient plate boundary is present along eastern margin of the Toyama Trough. However, the tectonic landform and geological structure characterized by the presence of active reverse faults indicate that Toyama Trough has been subjected to compressional stress.