考虑地形起伏和障碍体破裂的汶川地震强地面运动数值模拟

2008年5月12日四川汶川地区发生M_W7.9地震，震中位置103.4°E，31.06°N.这次地震造成了以汶川、映秀为中心及其周边地域建筑物的严重破坏和人员的重大伤亡，且因为高山等地形复杂区域抢险救灾的艰巨性，为及时救援造成很大干扰.为更好理解地形因素对于强地面数值模拟结果的影响，建立了包含地形起伏影响及去除地形影响的两类模型.同时，依据震源破裂过程运动学反演结果，建立了包含障碍体破裂过程的震源滑动模型，实现断层分段、空间倾角以及滑移角的动态设定.基于动力学的地震动模拟方法，通过对地震波传播过程的数值计算和后处理分析，模拟由地震激发的区域强地面运动过程.结果显示：（1）强震动台站的断层距对地形效应具有放大或抑制作用，距离断层破裂带越近，地形效应越明显，反之，距离越远，则地形效应越微弱；（2）因为地形高差与障碍体的影响，地震造成的峰值可能出现在震中区域之外；（3）考虑地形影响模型的地表峰值速度（PGV）区域位于汶川与北川附近；而未考虑地形影响模型的PGV区域位于灌县—江油断层的后半段，处清平、安县附近；对汶川地震近实时强地面运动波场的模拟、峰值图谱的圈定及未来大地震强地面运动特征的预测都有重要指示意义.

Numerical simulation of the strong ground motion of the 2008 Wenchuan Earthquake incorporated with topography and barrier rupture model

The M_W7.9 Wenchuan earthquake occurred in the Wenchuan area of Sichuan Province on May 12, 2008, at a location of 103.4°E and 31.06°N, and caused severe building damages and heavy casualties in Wenchuan, Yingxiu and their surrounding areas. Because of the complex mountainous terrain, timely rescue was difficult. In order to better understand the influence of topographic factors on the numerical simulation of strong ground motion, two kinds of models are established, one with complex topography effect and the other without. Additionally, according to kinematics inversion of source rupture, we incorporate earthquake source rupture model with asperity and barrier models. We also implement the spatial-temporal variations of fault segmentation, inclination and slip rake angles in the simulations. Based on the dynamic simulation of the ground motion, numerical calculation of seismic wave propagation and post-processing analysis, we simulate the ground motion induced by earthquake. The results show that: 1) the topographic effect varies with the distance between fault and strong motion station. The closer the distance is, the more obvious the topographic effect is, vice versa. 2) Due to the influence of topography, the peak of ground motion may occur outside the epicenter. 3) In model I, Peak Ground Velocity (PGV) distributions resulted from current simulation show much higher PGV values in the areas of Wenchuan, Beichuan than other places. In model Ⅱ, higher PGV area is located in the second half of the Guanxian-Jiangyou fault, near areas of Qingping, Anxian. The numerical modeling developed in this study has potential application in the ground motion prediction for the earthquake engineering. In addition, the numerical simulation could also be used to generate near-real-time shaking map in the implementation level.