JpGU-AGU Joint Meeting 2020

講演情報

[E] ポスター発表

セッション記号 S (固体地球科学) » S-SS 地震学

[S-SS04] 強震動・地震災害

コンビーナ:染井 一寛(一般財団法人地域地盤環境研究所)、松元 康広(株式会社構造計画研究所)

[SSS04-P20] Estimation of earthquake ground motions at MeSO-net stations

*若井 淳1先名 重樹1清水 惇1 (1.防災科学技術研究所)

キーワード:地震動、MeSO-net、微動、S波速度構造

In the past national project of Japan, “Metropolitan Seismic Observation network” (hereinafter, referred to as “MeSO-net”) was constructed for the investigation of the tectonic plate structures and earthquake ground motions in the Tokyo metropolitan area around ten years ago. The MeSO-net has about 300 stations with sensors installed around 20 meters underground in the area. Also, they are spatially distributed at intervals of 2 to 5 kilometers in the area.

In recent years, we have worked a subproject of “acquisition of spatially very-high-resolution earthquake observation data and development of the database by private-public partnerships” as a member in a national project or “Tokyo Metropolitan Resilience Project.” As one of the topics, we have tackled a challenge for estimation of seismic ground motions based on bore-hole seismic records observed at each MeSO-net station.

The point is as follows. First, a seismometer is installed on the ground surface at each station during two to three months and some earthquake observation records are obtained in addition to the bore-hole records at each station. And then, an observed frequency response function is obtained by calculating spectral ratios of the ground surface records to the bore-hole ones. Also, increment of seismic intensity is obtained by calculating that from the ground surface records and from the bore-hole records. At the same time, a miniature and centerless array microtremor measurement is performed at each station. This method of measurement can be adopted principally for estimation of an S-wave velocity structure in the surface ground. It consists of 4-point miniature array with a radius of 60 centi-meters and 3-point centerless array with around 10 meters on a side. An S-wave velocity structure is estimated based on a disperse curve of a phase velocity and an H/V spectrum calculated from microtremor data. And then it can be enhanced based on an observed frequency response function described above. Therefore, a transfer function can be obtained using 1-dimensional multiple reflection theory based on the S-wave velocity structure at a station.

In this project, we will develop the system for estimation of earthquake ground motions based on bore-hole seismic records by means of the a variety of amplification factors mentioned above. In this presentation, we will report on the results in the analyses of earthquake observation data and microtremor measurement ones at this moment.