Seismic response analysis of alluvial valley with two dipping layers by a boundary element-finite element coupling method

Abstract

A coupling process of time-domain boundary element method and finite element method is constituted for analysis of the dynamic response of an alluvial valley. Since the characteristics of these two methods are different from each other, the time increment of the boundary element method is set to be an integer multiple of the finite element method, and a combination of a linear interpolation of boundary element equations at two successive time steps with a finite element equation is proposed. Using this procedure, responses of alluvial valleys with two dipping layers are analysed for a vertically incident SV wave, and influence of the lower layer on these responses is investigated. It is found that the presence of the additional lower layer affects not only the reflected waves but also the surface waves. Furthermore, when an outcropping lower layer exists at the basin edges, the valley suffers an amplification of motion and an extreme increase in strains. These results show that a small difference in the layer at the basin edge is significant in analysing dynamic responses of an alluvial valley.