Forward prediction model of earthquake ground motion in sedimentary basins for seismic design of structures

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A direct 3-D boundary element method is applied to evaluate seismic waves in three dimensional sedimentary basin for incident SH, P, SV, and Rayleigh waves. We have utilized the Green's functions for an elastic half-space medium. Since the boundary conditions at the free surface of elastic media are automatically satisfied, the direct 3-D boundary element method is precisely formulated through those Green's functions based on the boundary conditions along a arbitrarily shaped soil interface. Numerical results of surface displacement amplitudes of a semi-spherical sedimentary basin for SH waves propagating nonvertically to the surface show good agreements with those results evaluated with the solution(Sanchez-Sesma et al., 1989)based on wave function expansions and an azimuthal decomposition. It should be noted that the present method is applicable to the scattering of not only incident body waves but also incident surface waves by a 3-D sedimentary basin whose soil interface is arbitrarily shaped, because a boundary element problem is formulated in terms of exact Green's functions which satisfy the free-boundary conditions on the half-space surface.