| 講演要旨(和文) | | 2003年宮城県北部地震の震源域で確認された周期約1秒の顕著な後続位相の発生メカニズムを明らかにするために，新色・山中(2011)で提案した3次元地下構造モデルを既往の研究資料を用いて修正し，周期1秒以下の短周期成分の評価ができる3次元地下構造モデルを構築した．構築したモデルで本震および余震による地震動シミュレーションを行うと，沖積層の盆地構造の影響と考えられる後続位相を明瞭に確認できた．これらの後続位相は地表に到達した実体波が，堆積層の不規則性によって表面波に変換され，地盤で増幅されながら平野を伝わったものであることがわかった． |
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| | 講演要旨(英文) | | During 2003 Northern Miyagi Prefecture Earthquake, the 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 motions in the area were affected by the sediments with a low S-wave velocity near the surface. Actually, the record of the main shock observed at Ishinomaki in the area shows a dominant peak of later phases at a period of 1 second. In order to clarify the mechanism of the characteristics, we tried to estimate the subsurface structure by waveform inversion of S-wave of the aftershock data observed by Yamanaka et al. [2004]. The estimated subsurface 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 the sediments. |
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