| 講演要旨(和文) | | この研究では，関東平野西部における鉛直アレイによる地震観測で得られたS波のスペクトル比のMCMC法による逆問題（Yamanaka et al., 2013）を行い，深部地盤の減衰構造のモデル化を試みた．関東平野西部のKiK-netの飯能と名栗観測点での地表と地中の観測点での約50個の地震記録からS波部分のスペクトル比を算出した．スペクトル比の逆解析では，佐藤・山中（2010）によるmisfitを用いてＭＣＭＣ法に基づいてモデルをサンプルした．サンプルされたモデルの頻度分布からS波速度とバイリニア型の減衰に関するパラメータ（佐藤・山中，2010）を同定した．Ｓ波速度は深いほど分解能が低下した．Ｑ値のパラメータは全層で同じであると仮定しており，高い精度での評価ができた．さらに，サンプルされたモデルに対する1次元増幅特性の計算結果から両地点とも増幅特性のばらつきは小さいことが分かった． |
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| | 講演要旨(英文) | | Spectral ratios of earthquake records in vertical borehole arrays at two sites of the KiK-net in Saitama prefecture in the western part of the Kanto basin were inverted to 1D profiles of S-wave velocity and Q-value of sedimentary layers for a reliable estimation of amplification factors at high frequency. We used the Markov Chain Monte Carlo method by Yamanaka et al. (2013) in the inversion to determine final model parameters with their resolutions. At first, earthquake data at the two KiK-net stations were analyzed for the spectral ratios between the surface and the bottom at a depth of -100 meters approximately of the boreholes. The spectral ratios were inverted to 1D-profiles. S-wave velocities and the parameters of Q-values for sampled models in the MCMC method show narrow frequency distributions indicating high resolutions. In particular the S-wave velocities for the shallow part have narrow distributions. We estimated S-wave amplification factors using the sampled models. Since the uncertainties for the S-wave velocities and the parameters for the Q-values are very small, the amplification factors of 1D S-waves are also stable with small fluctuations. |
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