Seismic velocity structure along the Sea of Japan with large events derived from seismic tomography for whole Japanese Islands including reflection survey data and NIED MOWLAS Hi-net and S-net data

Abstract

We conducted seismic tomography for entire Japanese Islands including the Sea of Japan and the Pacific Ocean using arrival times from reflection survey as well as the routine seismic network. We successfully imaged the shallow zone along the Sea of Japan from offshore Yamagata to the Noto Peninsula by using air gun data. An extremely low-V shallow zone is imaged between Sado Island and Noto Peninsula. We also obtained detailed seismic velocity structure beneath the Pacific Ocean at depths of 20–50 km using S-net data. The 2007 Noto Peninsula, the 2007 offshore Chuetsu, and the 2019 offshore Yamagata earthquakes occurred at the boundary between high-Vp and low-Vp zones. The west side of the hypocenter of the 2019 offshore Yamagata earthquake at depths of 10–30 km has high-V corresponding to the Mogami Trough. This high-V zone passes through Awa Island and reaches Sado Basin between Sado Island and Honshu. A major rift zone in the Tohoku Arc extending from the Akita region to the Niigata region along the coast of Sea of Japan corresponds to high-V lower crust and a shallow Moho. Graphical Abstract: [Figure not available: see fulltext.].