1997年玛尼地震对青藏川滇地区构造块体系统稳定性影响的三维DDA+FEM方法数值模拟

本文用三维非连续变形与有限元相结合（DDA+FEM）的方法，在青藏川滇地区三维构造块体相互制约的大背景中，通过用GPS资料做位移速率边界约束和震源机制约束，计算得到研究区的初始位移场和应力场与该地区GPS测量结果和震源机制分布结果基本一致.在此基础上进一步数值模拟1997年玛尼7.9级大震的发生过程，研究大震引起研究区各块体边界断层应力状态变化的特征.（1）发震断层两侧发生左旋走滑错动，最大水平位错大约7 m；（2）深部位错面上位错分布与用地震波资料震源反演的结果类似；（3）最大差应力变化等值线图与由星载D|INSAR技术获取的地表形变场图像相似；（4）地表垂直位移表明地震断层面略向北逆冲.计算模拟得到了玛尼地震发生引起青藏川滇地区构造块体系统各边界断层上库仑破裂应力变化的分布，表明玛尼大震的发生除了使其发震断层的两端库仑破裂应力增大，应力进一步集中外，位于上地壳层上东昆仑断裂中段的2001年昆仑山8.1大震（H=11 km）发震断层段的库仑破裂应力增加约2 MPa，位于中地壳层上喀拉昆仑断裂带中的2008年改则6.9级地震（H=30 km）发震断层段的库仑破裂应力也增加约0.7 MPa，可见这两个已接近破裂强度地段的失稳对发生大震起了一定促进作用.研究结果也表明：作者发展的三维DDA+FEM方法能有效地用于大震活动与各构造块体相互作用关系的研究.

3-D numerical simulation on influence of 1997 Mani earthquake occurrence to stability of tectonic blocks system in Qingzang and Chuandian zone using DDA+FEM method

Using 3-D Finite Element Method combined with Discontinuous Deformation Analysis, in large background of interaction among 3-D tectonic blocks in Qingzang and Chuandian zone, based on the GPS data and seismic focal mechanism, we compute initial displacement field and stress field in the studied zone, which agree basically with the results of GPS measurement and seismic focal mechanism distribution. Further the occurrence process of 1997 Mani earthquake with magnitude M_s7.9 is simulated numerically, and feature of stress state change on each boundary fault of blocks is studied. (1) The maximum horizontal dislocation is 7 m with left rotation and strike;(2) The distribution of dislocation on vertical face of the seismic fault is totally similar with the inversion result from seismic wave information; (3) Maximum shear stresses contour is similar with the deformation field from D-INSAR; (4) The vertical displacement distribution computed on the surface across fault indicates that the fault sliding is adverse to north. Furthermore, distribution of Coulomb failure stress change on the boundary faults of Qingzang and Chuandian block system after Mani earthquake is calculated. It indicates that the Mani earthquake, except making Coulomb failure stress increase and stress concentration in ends of the seismic fault, causes Coulomb failure stress in upper crust layer to increase about 2MPa at the seismic fault where Kunlun Shan M_s.9 earthquake (H=11 km) located at mid section of eastern Kunlun fracture occurred in 2002. and causes Coulomb failure stress in middle 〖JP2〗crust layer to increase about 0.7MPa at the seismic fault where Gêrzê M_s6.9 earthquake (H=30 km) 〖JP〗located at Karakorum fracture zone occurred in 2008. It seems to indicate that Mani earthquake has positive function to the two zones close to rupture strength and afterward occurrence of the two earthquake. The research results also indicate that 3-D DDA+FEM method developed by authors is available to apply in studying relationship between large earthquake occurrence and interaction of tectonic blocks.