三维复杂山谷地形SV波垂直输入地震反应分析

本文基于显式有限元法研究了地震波垂直入射时三维复杂山谷地形对地震地面运动的影响,在数值分析中应用了三维化二维的解法和黏弹性人工边界的处理方法,实现了地震波垂直输入下三维复杂场地地震动数值模拟,并验证了该方法的合理性.以四川桃坪地区一山谷地形作为研究对象,基于地表高程数据分别建立了二维和三维场地模型,对比研究表明:在复杂地形情况下考虑二、三维模型时具有明显差异,三维模型能更真实地反映地形变化对地震动的影响,复杂地形条件下有必要考虑三维实际场地模型.本文对边界自由场的处理方法也可用于处理三维复杂场地地震动斜入射问题,为三维复杂地形场地地震效应研究提供参考.

The seismic response analysis of three-dimensional Canyon complex topography under incident SV seismic waves

It has long been known that surface topography can have significant effect on seismic motions, and the numerical simulations are important tools for study on the complex topographic effect. Most applications of viscous-elastic artificial boundary assumed that the boundary is regular, however this is not the case, and the computational error will inevitably increase. In this paper, a simplified seismic input method was proposed, which is based on the explicit finite element method with viscous-elastic artificial boundary conditions and the two dimensional solution for three-dimensional problems. The numerical results from the homogeneous half-space model indicated that the wave input method is reasonable. We also establish a three-dimensional (3D) canyon model and four two-dimensional (2D) canyon models according to the real ground elevation data of steep topography in Taoping, Sichuan province, China. The seismic response of the five models in the case of SV wave vertical incidence is studied. Among them, the seismic input of the four 2D canyon models uses the conventional method, while the method introduced in this paper is applied in the 3D canyon model. The results show that it is necessary to establish a 3D model instead of 2D model according to the real ground elevation data. The calculating method of lateral boundary's free field for 3D complex topography is presented in this paper to provide a reference for the seismic effect of 3D complex terrain, and it can also be used to deal with the seismic oblique incidence in 3D complex terrain.