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