The Effect of Layered Medium on Rupture Process
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摘要: 震源动力学中破裂产生的地震动在层状介质中的传播模拟，是地震学以及地震工程学研究的前沿课题之一。本文通过建立精确的三维模型，选取具备灵活网格、高精度高效率计算性能的谱元法，利用有效抑制伪震荡的时间域离散方法——加权速度Newmark方法以及多次透射人工边界条件，进行了SCEC/USGS基准项目中TPV5模型的地震破裂过程模拟，得到基于层状介质模型和均匀介质模型（后者采用相同破裂模型）的埋深2km的震源参数结果。将二者进行对比，并具体分析破裂面位错、地震矩、破裂传播时间、上升时间和地表位移，发现层状介质对破裂过程的传播影响较为明显：① 层状介质的存在整体增加了破裂面上的位错，在层状介质模型下计算得到的地震矩约是均匀介质模型结果的1.3倍，因此认为层状介质增强了地震破裂过程中的能量释放；② 层状介质的存在使得破裂传播至地表的速度减慢，并缩短了地表各点的上升时间，增强了地表的地震动响应；③ 层状介质对于地表位移有着明显的增加作用，同时协同破裂面上的初始应力异常区域对位移峰值中心的改变有显著影响。④ 介质分异面附近地震动强烈。对结果进行整理后发现，在具有地下层状介质的地区要充分考虑层状介质产生的场地效应，否则可能会低估该地区的地震危险性。Abstract: The propagation simulation of ground motion caused by dynamic rupture is one of the most frontier topics in the field of earthquake and earthquake engineering research. Through three-dimensional models based on the spectral element method, which combines the flexibility in terms of mesh just like the finite element method with the accuracy like the pseudo spectral method as well as the computation efficiency, seismic rupture process in layered medium is simulated with Weighted Velocity Newmark Scheme and multiple transmitting artificial boundary condition in TPV5 model of the SCEC/USGS Spontaneous Rupture Code Verification Project. The results of layered medium and uniform medium are compared in terms of dislocation of fracture surface, earthquake moment, time of rupture propagation, rising time and surface peak displacement. The analysis shows that the layered medium can exert a great influence on earthquake rupture propagation:① The dislocation of fracture surface in layered medium is larger than that in the uniform counterpart, and the earthquake moment in layered medium is about 1.3 times as that of uniform medium, which indicates that layered medium intensifies the release of energy during rupture processes. ② Layered medium slows down the propagation of rupture to ground surface, shortens the rising time of various points on the ground surface and amplifies surface ground motion responses. ③ Layered medium results in the magnification of surface displacements, and changes the location of peak surface displacements together with stress anomaly on faults.④ There are strong ground motion near the surface of layered medium. Our results suggested that the site effects of layered medium should be carefully considered in order to avoid underestimating the seismic hazard in areas with layered medium. These conclusions mentioned above can provide implications for the seismic hazard mitigation of the region with layered earth medium.
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Key words:
- Dynamic rupture /
- Spectral element method /
- Layered medium /
- Site effects
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图 2 均匀介质模型
（a）与埋深2km的层状介质模型（b）中断层面上位错等值线分布对比图
Figure 2. The contour map of dislocation on the fault plane in the uniform medium (a) and in the layered medium (b)
图 3 深度为2km的异常带位错放大图
Figure 3. The magnification effect of anomaly zone at the depth of 2km
图 4 均匀介质模型
（a）与埋深为2km的层状介质模型（b）中破裂传播时间等值线对比图
Figure 4. The contour map of wave propagation time in the uniform medium (a) and in the layered medium (b)
图 5 均匀介质模型
（a）与埋深为2km厚的层状介质模型（b）的上升时间等值线对比图
Figure 5. The contour map of rising time in the uniform medium (a) and in the layered medium (b)
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