SV波全反射作用下地震动的合成及振动特性

Synthesis and vibration characteristics of ground motionsunder the excitation of total reflected SV waves

越来越多的研究表明来自基岩的地震波并不是垂直地面向上传播的。地震波在斜入射与垂直入射时所产生的场地效应有很大不同,由于存在全反射现象,SV波在斜入射时产生的场地效应更为复杂。文章基于均匀弹性半空间地震波传播理论,分别推导得到SV波入射角在小于、大于等于临界角时地震动的计算表达式,通过模型算例研究SV波全反射作用下的地震动特性。研究发现:由SV波产生的地震动主要由入射波和反射波构成,滑行波作用可以忽略;地面运动轨迹具有面波旋转振动特点;随着入射角的增大,地面震动从以水平方向振动为主逐渐过渡到以垂直方向振动为主,两个方向的振动均小于入射波峰值的2倍。

Research has shown that the propagation direction of seismic waves from bedrock is not perpendicular to the ground surface.The site effect generated by obliquely incident seismic waves is quite different from that generated by vertically incident seismic waves.The site effect under obliquely incident shear vertical(SV)waves is more complicated than that under vertically incident SV waves on account of the existence of total reflection.In this study,a set of mathematical expressions of ground motions was derived based on the theory of homogeneous elastic half-space seismic wave propagation when SV incident angles were less than,greater than,or equal to the critical angle.The mathematical expressions were then applied to a model example to calculate and analyze the ground motion characteristics under the excitation of total reflected SV waves.The results show that the ground motions generated by SV waves are mainly composed of incident and reflected waves,and the effect of sliding waves could be ignored.The ground motion trajectory exhibits the characteristics of rotational vibration of surface waves.With the increase in the incident angle,the ground horizontal vibration gradually decreases,whereas the ground vertical vibration gradually increases,but neither of them is greater than twice the peak value of the incident wave.