利用粘弹性球体位错理论研究2011年日本M_W9.0地震引起的震后位移时空变化

Post-seismic Displacements Induced by the 2011 Tohoku-Oki M_W9.0 Earthquake based on Visco-elastic Spherical Dislocation Theory

基于2011年3月~2015年9月的GPS观测数据,研究了2011年日本M_W9.0地震引起的震后位移时空变化,分析震后4.5a内震后断层余滑和粘滞性松弛对震后位移场的贡献。基于子断层叠加的思想,对Tanaka的粘弹性球体位错理论配套计算程序(环型解部分)加以改进,克服其近场计算精度不足(甚至错误)的缺陷,提高了近场震后位移的计算精度。利用弹性球体位错理论配套计算程序和改进后的粘弹性球体位错理论配套计算程序,分别计算2011年日本M_W9.0地震产生的同震位移,两组结果的差异仅占信号的1%左右,验证了对粘弹性球体位错理论配套计算程序改造的正确性。最后,结合震后3~4.5aGPS观测数据,利用Tanaka的粘弹性球体位错理论确定了2011年日本M_W9.0地震震中周边区域地幔粘滞性系数,其最佳拟合值为6×10^(18)Pa·s。

Abstract： In the present study, we extracted the post-seismic displacements caused by the 2011 Tohoku-Oki Mw9.0 earthquake from GPS observations. The data spans from March 2011 to September 2015. We studied the contributions of afterslip and visco-elastic relaxa- tion on the post-seismic displacements within 4.5 years after the main shock. We updated the software of Tanaka using a segment-summation scheme, improving the computation accuracies in the near-field. We calculated the co-seismic Green functions of the vertical and horizontal displacement at the source depth of 32 km, using the visco-elastic disloca- tion theory of Tanaka and elastic spherical dislocation theory of Sun, respectively. The results indicate that these two sets of Green functions are consistent with each other. The differences between the two sets of Green functions are within the uncertainty of the computation. This fact confirmed the correctness of our new software. Then we simulated the post seismic displacements from March 2014 to September 2015, which are mainly caused by the visco-elastic relaxation of the Mantle. Comparing the observed displacements with the simulated ones, we found that the optimal viscosity of the Mantle around the epicenter region is about 7 × 10^18 Pa· s.