汶川大地震震后重力变化和形变的黏弹分层模拟

Simulation of post-seismic gravity change and deformation of the Wenchuan earthquake based on viscoelsatic layered half-space model

基于有限矩形位错理论及陈运泰等、JiChen等通过地震波反演的断层模型,结合研究区地壳—上地幔平均波速分层结构,利用PSGRN/PSCMP软件模拟计算了黏弹分层半空间中汶川地震(MS8.0)产生的同震及其震后地表形变和重力变化,同时给出了震后形变和重力变化的年变化率.模拟结果表明,同震形变和重力变化显示出发震断层倾滑逆冲兼具右旋走滑综合特征;其变化主要发生于断层在地表的投影区附近,震后地表重力变化和形变量均不断增大,影响的范围也不断扩张;震后50a间近场年均形变量可达10mm,年均重力变化量可达2×10-8m/s2,而远场年均形变量一般低于2mm,年均重力变化量一般低于0.4×10-8m/s2;形变和重力变化在震后200a内变化较为显著,变化率逐渐减小,水平位移在400a后基本稳定不变,垂直位移、重力变化和大地水准面变化在800a后基本稳定不变.

Using the PSGRN/PSCMP software and the fault model used in seismic wave inversion offered by Chen Yuntai et al and Ji Chen et al, based on the finite rectangular dislocation theory and local layered wave velocity structure of the crust-upper-mantle, surface co- and post-seismic gravity change, deformation and geoid change caused by the MS8.0 Wenchuan earthquake are simulated, and the annual variation rate is also computed. The simulation results indicate that： the co-seismic gravity change and deformation show that the earthquake fault is of the characteristics of thrusting and right-lateral strike-slip. The gravity change and deformation mostly occur on the surface of the fault projection plan, and are increasing after the earthquake, with the influence extent being expanding. The annual average near-field deformation can reach to 10 mm during the 50 years after the earthquake, and the annual average gravity change is 2×10^-8 m/s^2. To the far field, these annual variation are less than 2 mm and 0.4×10^-8 m/s^2, respectively. The post-seismic deformation and gravity change increase significantly during the first 200 years. The change rate becomes smaller and smaller. Horizontal displacements will come to be stable 400 years later. Vertical displacement, geoid and gravity change will exist until 800 years after the earthquake.