SEGJ Technical Conference

Estimation of shallow S-wave velocity structures in the middle part of Ibaraki prefecture, using microtremor exploration

Abstract For the purpose of estimation on the shallow part of S-wave velocity structure in the Higashi-Ibaraki Terrace, where strong ground motion was observed during the 2011 off the Pacific coast of Tohoku Earthquake (Mw.9.0), we conducted microtremor array measurements. The phase velocity exhibits high in the western part, while low velocity in the middle of the Higashi-Ibaraki Terrace. The inversion of phase velocities revealed the S-wave velocity in the area. The depth to the engineering bedrock, which has more than 450 m/s, was deep in the middle of the Terrace. The 30m Average S-wave velocity (AVS30) exhibits large variation in the Terrace. The amplification at IBR013 exhibits high in the high-frequency and that in the middle or close to the coastline exhibits high in the low-frequency in the Higashi-Ibaraki Terrace.