基于GPS观测值研究日本M_W9.0地震震后形变机制

基于GPS观测的震后水平位移对2011年日本MW9.0地震的震后形变特征进行研究。震后近5a(截至2015-12),震后水平位移累积达到东向60~165cm,南向20~65cm,距离震中较远处的G104、G105及J192站点观测到的震后位移累积变化已超过同震位移,且震后形变还在持续。联合震后余滑和粘弹性位错理论模拟震后形变,利用这2种作用机制对震后GPS水平形变进行解释。研究表明,震后余滑在震后形变最初阶段起主要作用,但随着时间增长而逐渐衰减,粘滞性松弛作用的贡献随着时间增长而变大,GPS观测到的震后地表形变可由这2种机制结合得到较合理的解释。利用震后GPS形变模拟估算地震区域的地幔粘滞系数在1.5×1019 Pa·s量级。

Study on the Post-Seismic Deformation Mechanism Caused by the MW9.0 Japan Earthquake Based on the GPS Observation

The post-seismic deformation characteristics of the MW9.0 Japan earthquake are studied based on GPS observation. The post-seismic horizontal displacements observed by GPS accumulated to 60~165 cm for the east component, and 20~65 cm for the south component, in nearly 5 years following the main shock, until December 2015. For GPS sites further away from the epicenter, the post-seismic displacements have exceeded their co-seismic changes. Moreover, the post-seismic deformation is still continuing. According to the theories of afterslip and viscoelastic dislocation, the post-seismic deformation is simulated and the GPS observations are explained by these two mechanisms. The simulation results indicate that afterslip plays a major role in the initial stage of post-seismic deformation, but it shows an exponential decay with time. On the contrary, the contribution of viscoelastic relaxation increases with time. The results also suggest that post-seismic deformation can be reasonably explained by combining these two mechanisms. In addition, the mantle viscosity in the seismic area is inferred to be of the order of 1.5×1019 Pa·s from post-seismic deformation observed by GPS.