| 講演要旨(和文) | | 2003年宮城県北部地震は震源域付近に既設地震観測点がないために，震源域では地震動特性は明らかではない．同地域の石巻での本震の記録を見ると，周期約１秒程度の後続位相が確認された．その発生メカニズムを明らかにするために，山中・他(2004)による余震観測のデータを用いて，鈴木(2009)によるS波初動部に着目した波形逆解析から地下構造の推定を試みた．推定された地下構造は地域性を表し，推定される波形もうまく観測波形の特徴を説明できた．そこで，推定された地下構造を重力異常値(地質調査所2000)で内挿し3次元地下構造モデルを作成し，差分法による3次元地震動シミュレーションを行った．周期１秒以下の短周期成分を評価できるよう，本学スーパーコンピュータTSUBAMEを用いて数百CPUの並列規模で行うと，速度の遅い表層地盤内での重複反射により振幅が増大された後続位相が確認できた． |
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| | 講演要旨(英文) | | In 2003 Northern Miyagi Prefecture Earthquake, damage of wooden houses was observed in the focal area. The ground motion characteristics in the focal area are not clearly understood, because there are a few seismic stations near the focal area. It is expected that the ground motion in the area were affected by the sediments with low S-wave velocity near the surface. Actually, the record of the main shock observed at Ishinomaki in the area shows a 1-sec period dominant peak of later phases. In order to clarify the mechanism of the characteristics, we tried to estimate the underground structure by waveform inversion of S-wave of the aftershock data observed by Yamanaka et al. [2004].Estimated Underground structure represents locality according to surface geology, Therefore, we made a 3D subsurface structure model from the inversion results with gravity anomaly [GSJ, 2000].We, then, simulate ground motion by finite difference method, using the subsurface structure model. We found the significant later phases in the synthetic motions and concluded that the later phases in the 2003 Northern Miyagi Prefecture Earthquake is surface waves converted from S-wave by the irregularity of sediment. |
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