Studying the Effects of U-Shaped Canyons and Underground Cavities Interaction on the Surface Ground Motion Due to SV and P Waves by BEM

Due to the complexity of scattering issues by topographical features above subterranean cavities, few studies have been conducted in this field. In this regard, a 2-D scattering and diffraction of in-plane P and SV waves induced by a U-shaped canyon above underground cavities is proposed herein to account for the topographic effect of such a canyon. To show the interaction between U-shaped canyons and underground cavities or underground holes like natural karstic cavities and their effects on the surface ground motion, a parametric analysis is carried out in the time-domain by BE method. The important parameters considered in this parametric study include: the width of the underground cavities; the cavity depth; the depth and radios of cavity and shape of canyon. The results indicate the following: (1) different incident waves are caused different amplification pattern; (2) the presence of underground cavities may change the surface motion field significantly; (3) the strong ground motion amplitude appears to be very sensitive to the frequency of incoming waves and depends on size and shape of the canyoncavity system, and generally seismic interaction between them.