不整形性を有する沖積地盤の地震観測シミュレーション : BEMとFEMの結合解法による解析

概要

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Amplification of ground motion due to diffraction and scattering of plane harmonic body waves by layered soft soils of Hikichi River alluvial valley, at which a series of earthquake observation tests have been conducted, is investigated by using a combined method of finite and boundary elements. The alluvial valley is modeled as a set of irregular dipping layers embedded into an elastic half-space. Amplification functions, accelerograms and Fourier spectra at the ground surface are evaluated for vertically incident SH, SV and P waves and comparisons are made with the observed data. It is found that the calculated results show a fairly good agreement with the observed ones. Numerical results also demonstrate that the presence of the alluvial valley may cause very large amplification of the surface ground motion and that the amplification function becomes more complicated compared with the result of simple one-dimensional analysis. It is worthy of note that a considerable vertical ground motion is induced by a vertically incident SV wave by the presence of the alluvial valley.
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