Influence of actual topography on the source dynamic rupture process and strong ground motion of the 2010 Yushu MS7.1 earthquake
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摘要: 基于震源动力学模型，采用曲线网格有限差分法模拟了水平自由地表及实际地形条件下2010年玉树MS7.1地震的震源破裂过程及相应的地面地震动，获取了断层面上的破裂传播过程、最终滑移量分布及峰值地面速度分布，讨论了实际地形对玉树地震破裂过程及相应地震动的影响。基于本文设定的动力学模型，模拟结果显示：断层面上的高应力降是玉树地震出现超剪切破裂传播现象的主要原因；计算区域的实际地形阻碍了由自由地表引起的超剪切破裂的产生，对断层面滑移量的分布特征及滑动速率影响较大，进而在一定程度上降低了地震动峰值，同时对地震动的分布特征产生影响，且地震动平行断层面的水平分量相对受影响更大。Abstract: Based on the source dynamic models, the curved grid finite-difference method was implemented to simulate the dynamic rupture process and the resultant ground motions of the 2010 MS7.1 Yushu earthquake with horizontal free surface and actual topography respectively. Then the rupture propagation, final slip distribution and distribution of peak ground velocity were obtained to investigate the effect of actual topography on the dynamic rupture process of the Yushu earthquake and the resultant strong ground motions. Based on our models, the results show that the super-shear rupture occurred during the rupture propagation process, which was mainly induced by high stress drop on fault plane. The actual topography has prevented the generation of super-shear induced by free surface and has a great influence on the final slip distribution and slip rate on fault plane, then will affect the characteristics of ground motions as well as reduce the peak values of ground motions to a certain extent. The fault-parallel component of ground motion is relatively more affected. The investigation about the fault rupture dynamics will help us to understand well about the source rupture process and explain the characteristics of its strong ground motions, which is of great significance to more reasonably predict the ground motions of possible destructive earthquakes in the future.
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图 1 模拟计算区域（矩形）及破裂起始点在地表的投影位置（红色圆点）示意
Figure 1. Location of the simulation area （rectangle frame） and surface projection of rupture initial point （red dot）
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图 2 计算区域实际地形
红色圆点表示破裂起始点在地表的投影位置，红色实线表示断层迹线
Figure 2. Actual topography of computational area
The red dot indicates surface projection of the rupture initial point and the red line indicates the fault trace
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图 3 断层面初始应力分布（图中数字表示不同应力分布区域的编号）
Figure 3. Distribution of initial stress on fault plane
The numbers in the fig. indicate the serial numbers of areas with different stress distribution
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图 4 水平自由地表模型（模型Ⅰ，a）和实际地形模型（模型Ⅱ，b）中断层面上最终滑移量分布
Figure 4. Distribution of final slip on fault plane for horizontal free surface model （model Ⅰ ，a） and actual topography model （model Ⅱ ，b）
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图 5 水平自由地表模型（模型Ⅰ，a）和实际地形模型（模型Ⅱ，b）中断层面上滑动速率快照
Figure 5. Snapshots of slip rate on fault plane for horizontal free surface model （model Ⅰ ，a） and actual topography model （model Ⅱ ，b）
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图 6 水平自由地表模型（模型Ⅰ，a）和实际地形模型（模型Ⅱ，b）中破裂起始点深度上沿走向方向滑动速率随时空变化图像
Figure 6. Time-space plot of slip rate at the hypocentral depth along strike for horizontal free surface model （model Ⅰ ，a） and actual topography model （model Ⅱ ，b）
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图 7 水平自由地表模型（模型Ⅰ，a）和实际地形模型（模型Ⅱ，b）中地面质点振动速度平行于断层面的水平分量快照
Figure 7. Snapshots of fault-parallel component of particle velocities for horizontal free surface model （model Ⅰ ，a） and actual topography model （model Ⅱ ，b）
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图 8 水平自由地表模型（模型Ⅰ，左侧）和实际地形模型（模型Ⅱ，右侧）中峰值地面速度三分量分布
（a） 垂直于断层面的水平分量；（b） 平行于断层面的水平分量；（c） 垂向分量
Figure 8. Three components of peak ground velocity distribution for horizontal free surface model （model Ⅰ ，left） and actual topography model （model Ⅱ ，right）
（a） Fault-normal component；（b） Fault-parallel component；（c） Vertical component
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图 9 均匀初始应力下水平自由地表模型（模型Ⅲ，a）和实际地形模型（模型Ⅳ，b）中断层面上滑动速率快照
Figure 9. Snapshots of slip rate on fault plane with uniform initial stress for horizontal free surface model （model Ⅲ ，a） and actual topography model （model Ⅳ ，b）
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图 10 障碍体区域6的屈服应力降至5σu时水平自由地表模型（左侧）和实际地形模型（右侧）中断层面上最终滑动量分布
Figure 10. Distribution of final slip on fault plane for horizontal free surface model （left） and actual topography model （right） when the yield stress of the barrier region 6 drops to 5σu
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图 11 水平自由地表模型（左侧）和实际地形模型（右侧）中断层面上破裂起始点深度上沿走向方向滑动速率随时空变化图像
Figure 11. Distribution of time-space of slip rate at the hypocentral depth along strike on fault plane for horizontal free surface model （left） and actual topography model （right）
表 1 断层面上各区域应力参数
Table 1 Stress parameters for the areas on fault plane
区域 初始剪切
应力$ {\sigma }_{0} $ 
剪切破裂
强度${\sigma }_{{\rm{u}}}$ 
临界滑动弱化
距离Dc/m1 1.01 1.0 0 2 0.60 1.0 0.15 3 0.96 1.5 0.15 4 0.72 1.2 0.15 5 0.20 16.0 40.0 6 0.20 16.0 40.0 7 0.20 16.0 40.0 断层其它区域 0.49 1.0 0.15 断层外 0.20 200.0 40.0 
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