基于GPS观测值研究日本Mw9.0地震震后形变机制

摘要

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 postseismic 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.%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5 a(截至2015-12),震后水平位移累积达到东向60～165 cm,南向20～65 cm,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.