Three Dimensional Seismic Velocity Structure Beneath Japanese Islands From Sea of Japan to Pacific Ocean Including NIED S-Net Data

Date: 4/25/2019

Time: 04:00 PM

Room: Cascade II

1. Introduction

We investigate the 3D seismic velocity structure of the Japanese Islands including beneath the Sea of Japan and Pacific Ocean. NIED constructed Hi-net after the 1995 Kobe earthquake, S-net after the 2011 Tohoku-oki earthquake, and DONET constructed by JAMSTEC was transferred to NIED in April 2016. We apply the seismic tomography for arrival time data detected by these networks operated by NIED as well as other organizations.

2. Data and method

The target region, 20-48°N and 120-148°E, covers the Japanese Islands. In addition to the arrival time data used by Matsubara et al. (2017), we used P- and S-wave arrival times for 32952 earthquakes recorded at about 1500 stations including the NIED S-net and DONET from April 2016 to June 2018. We also added the arrival time data of events near the coast of the Sea of Japan detected at the stations operated by universities from 2000 to 2004. Totally 6356481 P arrival data and 3534482 S arrival data from 112631 events are available.

3. Result and discussion

We clarified the seismic velocity structure beneath the Sea of Japan at depths of 10-20 km from off Hokkaido to Wakasa Bay. Vp beneath the Sea of Japan is high at depths of 10-35 km. Vp along the coast of Sea of Japan in western Japan is moderate. The lithospheric velocity structure in this region is strongly affected by the mid-Tertiary break up and formation of the Sea of Japan. Through the reactivation of the younger compression, tsunamigenic source faults has been developed. The information of the lithospheric structure provides the essential information to the structure of faults.

Due to the contribution of S-net, the velocity structure of the overlying plate beneath Pacific Ocean has been improved. One important feature is the probable Mesozoic rift structure trending NS from the coast of Tohoku to the west of Hidaka collision zone. Recent the 2018 Iburi-Tobu earthquake (M6.7) may be related to the reactivation of the rift related structure in the upper mantle to the lower crust, where marked by high-Vp.

Presenting Author: Makoto Matsubara

Authors