| 講演要旨(和文) | | 2011年東北地方太平洋沖地震以降，首都圏での地震活動が増加しており，今後，立川断層等による活断層による被害地震の発生が危惧されるため，首都圏では精度の高い強震動予測が必要とされる．本研究では，立川断層における強震動予測のための3次元地下構造モデルの作成を目的として，立川断層帯周辺地域で微動アレイ観測を実施し，得られたレイリー波位相速度を用いて焼きなまし法による逆解析を実施することにより，立川断層帯周辺地域における深部および浅部のS波速度構造を推定した．解析の結果，深部地下構造における基盤深度は立川断層帯の東側において急激に深くなっており，その段差は概ね2km程度であった．また，浅部におけるS波速度構造は立川断層帯の東側において深部におけるS波速度とも調和的であった． |
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| | 講演要旨(英文) | | Tachikawa fault is one of the most activity faults in the Tokyo metropolitan area and when large earthquake will occur by this fault in the near future, it is expected that large economic and human loss will happen around this area. However, three dimensional subsurface structural model is not clear still enough for the estimation of the strong ground motions in this area. In this study, we estimated deep and shallow S-wave velocity structures using the Rayleigh wave phase velocities from the obtained records of the microtremor array explorations. Rayleigh-wave phase velocity at periods from 0.5 to 5.0 seconds from large array was estimated from a frequency-wave number spectral method analysis of the microtremors. And also Rayleigh-wave phase velocity at periods from 0.03 to 0.3 seconds from small array was estimated from a spatial autocorrelation method analysis of the microtremors. We identified the subsurface structural model using inversion based on the simulated annealing method. Based on numerical experiments it is indicated that thickness of individual layers are inverted very well. The results indicate that a basement depth in those profiles at down-thrown side of the fault is larger than that at up-thrown side with a difference of about 2km. |
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