Three-dimensional Scattering Of Elastic Waves Around An Alluvial Valley In A Saturated Layered Half-space

Landform of alluvial valley is one of the important local site conditions. Many observations and analyses of seismic disasters in our and foreign countries indicate that alluvial valley has great influence on the scattering of seismic waves, so studies on this field have important theoretical and practical value. Most of the present studies are based on the assumption that the natural soil is simplified as homogeneous,isotropic and elastic solid medium. However, the soil near the ground surface is mostly fluid-poroelastic and should be modeled by layered saturated medium to represent the inhomogeneity and two-phase property along its depth. Based on this background, this paper studies the scattering problem of P,SV and SH waves by the valley in homogeneous and layered 3-D saturated half-space.This paper uses indirect boundary element method to study the amplification effect on seismic wave by the valley in 3-D saturated homogeneous half-space and 3-D saturated layered half-space. The influence of incident angle, previous condition and porosity on surface amplitude of the valley in saturated homogeneous is discussed in details. By taking the model of single layer on bedrock for example, the influence of bedrock-to-soil stiffness ratio together with layer thickness on surface amplitude of the valley is also investigated in layered saturated half-space.Analysis in this paper indicates that parameters such as dimensionless frequency, incident angle, previous condition, porosity, layer thickness and bedrock-to-soil stiffness ratio lead to a great impact on seismic amplification. The displacement response of the valley in dry half-space is different from that in two-phase saturated half-space, and amplification effect in homogeneous saturated half-space varies much from that in layered saturated half-space.