Amplification Effects Of Seismic Waves By A Multi-layered Valley Site

As one of those important research topics in earthquake engineering and seismology,a remarkable amount of literatures have been reported to study amplification effects by a homogenous alluvial valley in a half-space.However,many geological factors(such as the river's sedimentary erosions and the river migration,etc.)may lead to multiple sedimentary layers in an actual valley while the study of site effects by a multi-layered sedimentary valley is still incomplete.Thus,it is of important theoretical significance and engineering guidance value to study the site effects caused by multi-layered valleys using a more rational model.Based on those previous studies,this paper improves the existing indirect boundary element method to study wave scattering of seismic-waves by a multi-layered valley in a layered half-space in this paper,and the article is organized as follows.Firstly,the scattered fields in the closed regions are constructed by using the full-space Green's functions and scattered fields in the opened layered half-space region using the layered half-space Green's functions,and the free fields of a layered half-space under incident plane SH-waves can be calculated by the direct stiffness method;The wave scattering problem of a multi-layered valley site can be solved by using the multi-domain IBEM.Secondly,we use the extension of the present multi-domain IBEM to study the diffraction of P,SV and Rayleigh waves by a multi-layered valley site.Besides,to investigate the effect of sediment sequence of the alluvial valley on the surface motions,cases of normal sequence,soft interlayer and inverted sequence are considered.The results show that the soft interlayer locating at the bottom of the valley has a good isolation effect on the high-frequency vibration;sedimentary sequence has a significant effect on the natural and predominant frequency of the ground motion;the change of sedimentary sequence may lead to the change of the dynamic characteristics,which in return affects the mechanism of dynamic interaction between alluvial valley and the layered site.As a reflection of the dynamic characteristics of the layered site,the existence of the soil layer changes the interaction among the scattering waves,reflection waves and the incident waves,leading to more complex variation on the displacement amplitudes.