震后GPS观测数据揭示的日本MW9.0地震周边地区地幔黏滞性结构垂向变化  

Variation of the mantle viscosity around the Tohoku-Oki M_W9.0 earthquake revealed by post-seismic GPS data

作　　者：陈飞 刘泰 付广裕[1] 佘雅文[1,3] CHEN Fei;LIU Tai;FU GuangYu;SHE YaWen(Institute of Earthquake Forecasting,China Earthquake Administration,Beijing 100036,China;Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;Hebei Earthquake Agency,Shijiazhuang 050021,China)

机构地区：[1]中国地震局地震预测研究所,北京100036 [2]中国地震局地球物理研究所,北京100081 [3]河北地震局,石家庄050021

出　　处：《地球物理学报》2020年第6期2210-2220,共11页Chinese Journal of Geophysics

基　　金：国家重点研发计划项目(2018YFC1503704);国家自然科学基金(41874003,41574071)联合资助.

摘　　要：本文利用大范围的震后GPS数据和黏弹性球形地球位错理论,定量研究了日本MW9.0地震周边地区地幔黏滞性结构的垂向变化.首先结合陆地和海底的GPS观测数据,以及基于球形地球位错理论格林函数和贝叶斯反演方法,反演了该地震的同震滑动分布,发现其最大错动量高达59m.然后在均一地幔黏滞性结构的假设前提下,确定了震源周边地区地幔黏滞因子的最优解,发现依据该地幔黏滞因子获得的理论远场震后位移和GPS观测结果之间的均方根误差高达0.81cm,不能解释远场观测结果.为解决上述问题,本文对震中周边地区地幔黏滞性结构沿垂向方向进行分层,建立了一个随深度变化的地幔黏滞性构造模型,然后综合利用远近场的GPS数据对该地区地幔黏滞因子进行反演研究,结果表明,震源周边地区岩石圈弹性层厚度最优解为40km,40~220km深度的地幔黏滞因子最优解为6×10^18Pa·s,220~670km深度之间的地幔黏滞因子最优解为1.5×10^19Pa·s.上述地幔黏滞性构造使远场的均方根误差降为0.12cm,仅为利用均一地幔黏滞性构造所得均方根误差值的15%,大大提高了远场模拟结果的准确性.最后,观测值和模拟值之间的均方根误差分析表明,近场震后形变数据主要约束浅层的地幔黏滞性结构,而远场震后形变数据主要约束深部的地幔黏滞性结构.In this paper,we research quantitatively the variation of the mantle viscosity around the Tohoku-Oki MW9.0 earthquake by using the post-seismic GPS data that is widely distributed,as well as the viscoelastic spherical earth dislocation theory.At first,combined land and seafloor GPS data,we inverse the co-seismic slip distribution of the Tohoku-Oki MW9.0 earthquake by using Bayesian inversion method as well as the Green′s functions of the spherical earth dislocation theory.The maximum of the slip is about 59 m.Then,under the assumption of a uniform model,we inverse the viscosity of mantle around the Tohoku-Oki MW9.0 earthquake.The root mean square error between the calculated post-seismic displacements and the observed ones reaches up to 0.81 cm in the far field.Next,we establish a model of the mantle viscous structure varying with the change of the depth,and inverse the viscosity of mantle in this region by using far-field and near-field GPS data.As a result,the optimal solution of the lithosphere thickness around the epicenter is 40 km.The optimal viscosity of the mantle between 40 km to 220 km is about 6×10^18 Pa·s,and changes to be 1.5×10^19 Pa·s between 220 km to 670 km.Such a viscous structure of mantle makes the root mean square error between the observations and calculations in the far field to be as small as 0.12 cm,about 15% of the one under the assumption of uniform mantle viscosity.The accuracy of the theoretical result is improved.Finally,the analysis of root mean square error between the observed value and the simulated value indicates that the near-field data of post-seismic deformation mainly constrain the viscous structure of the shallow mantle,while the far-field data of post-seismic deformation mainly constrain the viscous structure of the deep mantle.

关 键 词：日本MW9.0地震 球形地球位错理论 地幔黏滞因子(黏滞因子) 震后形变 岩石圈弹性层厚度(弹性厚度) 

分 类 号：P315[天文地球—地震学]