汶川震区地震动三维地形效应的谱元法模拟

Simulation of three-dimensional topographic effects on seismic ground motion in Wenchuan earthquake region based upon the spectral-element method

针对三维波动弹性动力方程推导了谱元法算法,并考虑三维真实地形及介质的衰减特性,基于并行计算环境采用谱元法和ASTER DEM模型对5.12汶川地震动的地形效应进行了模拟.模拟结果表明陡峻地形对地震波两个水平分量的影响要大于对竖向分量的.震中附近区域的PGA最大值为671cm/s2,高PGA区多分布于山顶及山脊区域.与平坦地形相比,PGA相对地形放大系数为-12%～110%,不同地点的z向速度分量波幅遵循峰顶、山脊得到放大或沟谷得到降低的模式.这说明与已有的二维概化模型计算结果相比,三维真实地形对地震动的影响比二维概化模型更为复杂.

The effects of topography on seismic ground motion of Wenchuan earthquake were simulated based upon elastodynamic equation for 3D wave propagation,the spectral-element method,ASTER DEM model and parallel computation environment and incorporated realistic 3D topography and attenuation of media.The simulated results show that topographic effects due to great rough terrain on two horizontal components of seismic wave are bigger than those on vertical component.The max PGA value in zone near epicentre is 671 cm/s2,while large PGA values are almost located near mountain tops and ridges.Compared with the model without topography,the relative topographic amplification factors of PGA in the zone near the epicentre are -12%～110%,while the z velocity component at different sites are in accordance with the pattern of amplification on mountain tops and ridges,and there is a decrease in valleys and brooks.It can be concluded that the effects of 3D realistic topography on seismic ground motion are more complex than those of the existing 2D generalized model.