利用GRACE卫星数据提取苏门答腊地震同震和震后重力变化

The Evolution Process of the Gravitational Field after the Sumatra Mw9.3 Earthquake from GRACE RL05 Data

基于GRACE重力卫星数据,采用P3M6去相关滤波技术、350km半径的高斯平滑技术与差分方法,提取2004年苏门答腊Mw9.3地震的同震和震后重力场时空演化过程。该地震断层下盘同震重力变化达到4.6μGal,上盘同震重力变化最大值为-8.3μGal,该结果与球体位错理论计算结果在量级和分布形态上具有较好的一致性。震后7a断层下盘重力变化累计达到5.6μGal,超过同震变化信号;而断层上盘震后重力变化只有0.6μGal,仅为同震变化信号的11%。该现象表明,断层下盘所在海洋地层的粘滞性较低,地层相对柔软,其地层在震后由于较大的粘滞性松弛效应而持续变形,并伴随较大的重力变化;而断层上盘所在的地层接近陆地地壳特性,地层相对脆硬,震后受地层的粘滞性响应而导致的重力变化相对较小。

Based on the GRACE data,we successfully extract the co-seismic and post-seismic gravity changes caused by the 2004 Sumatra Mw9.3 earthquake,using P3M6de-correlation filtering,Gaussian smoothing with a 350km radius,as well as the difference method.The peak co-seismic gravity changes in the uplift and subduction zones reach up to 4.6 and-8.3μGal,respectively.Such results agree well in both magnitude and distribution with those calculated by the dislocation theory for a spherical earth model.The total post-seismic gravity changes of 7 years are up to 5.6μGal in the uplift zone,which is bigger than the corresponding co-seismic gravity changes.On the other hand,the changes in the subduction zone are only 0.6μGal,just about 11% of corresponding co-seismic gravity changes.Our results imply that the viscosity of the marine strata in the uplift zone is relatively lower than in the strata of the subduction zone.It is the low viscosity in marine area that caused the continuous deformation and relatively bigger gravity changes after the earthquake.The little post-seismic gravity changes in the subduction zone imply the high viscosity of the continental strata.