3-D Scattering of Obliquely Incident Plane PWaves by Alluvial Valley Embedded in Layered Half-Space

The indirect boundary element method （IBEM） was established to solve the problem of 3-D seismic re- sponses of 2-D topographies, by calculating the free-field responses with the direct-stiffness method and simulating the scattering wave fields with the dynamic Green＇s functions of moving distributed loads. The proposed method yields accurate results, because the 3-D dynamic stiffness matrixes used are exact and the fictitious moving distributed loads can be acted directly on the interface between the alluvial valley and the layered half-space without singularity. The comparison with the published methods verifies the validity of the proposed method. And the numerical analyses are performed to give some beneficial conclusions. The study shows that 3-D scattering by an alluvial valley is essentially different from the 2-D case, and that the presence of soil layer affects not only the amplitude value of surface dis- placements but also the distribution of surface displacements.