Scattering Of The 3D Local Complex Topography In Transversely Isotropic Site For Incident Seismic Waves

Scattering of seismic waves by the local complex site has always been the subject of both earthquake engineering and structural seismic design.Since the 70 s of last century,numerous scholars have devoted to great effort on this problem with different methods.But one can find that most of the existing researches are limited in the assumed isotropic medium with ignoring the anisotropy character of the soil.Considering the transversely isotropic(TI)properties of the media could be more consistent with the practical engineering,when the elastic medium of natural soils exhibiting significant differences between the horizontal and vertical direction during sedimentation and weathering.Based on those previous studies and by taking three dimensional basin and hill in layered TI half-space,the scattering and diffraction problems of local complex site are studied with the help of the indirect boundary element method(IBEM),which related with the improved green's functions for uniformly distributed inclined plane.The main contents are as follows:Firstly,by introducing two potential functions and employing the Fourier expansion and Hankel transform,the dynamic response of every observation point under concentrated load can be derived.Secondly,the green's functions for uniformly distributed load applied on the inclined plane are obtained by surface integral,and the scattering problem of local complex site for incident seismic waves is solved by IBEM.Finally,several impact factors on surficial response,such as anisotropic degree of the media,depth of the valley,shape of the hill et al.,are considered in detail.Result shows that the variation of TI parameters,depth of the valley and shape of the hill change the dynamic characteristics of the site,which further causing the difference of the displacement amplitudes.The degree of material anisotropy has little effect on the amplitudes when the incident frequency is less than 0.25,as the frequency reaches 0.5,the influence on the amplitudes gradually emerges;There is litter scattering effect on the surrounding ground for the shallow valley,but as the incident frequency increases,its amplitudes usually bigger than those of the other two different alluvial valleys;The ground motion at the foot of the protruding hill is smaller than that of the surrounding surface for the Gaussian shaped hill,but 40%~60% bigger for the hemiellipsoidal and paraboloidal shaped hills,especially for incident qSV-and SH-waves.