联合GPS和GRACE观测研究日本MW9.0地震震后变形机制

联合GPS和GRACE观测研究日本MW9.0地震震后变形机
制
梁明;王武星;张晶
【期刊名称】《地球物理学报》
【年(卷),期】2018(061)007
【摘要】Post-seismic deformation characteristics of the MW9.0 Tohoku-Oki earthquake are studied by using GPS and GRACE observations.GPS continuous observations show that the regional post-seismic displacements are characterized by exponential function,and the rate of change accords with the attenuation characteristic of the Omori formula.Post-seismic horizontal displacements accumulated to 60～165 cm for the east components,and 20～65 cm for the south components,in nearly 5 years following the main shock,until December 2015.For GPS sites further away from the epicenter,post-seismic displacements have exceeded their co-seismic changes.Moreover,their post-seismic deformations are still continuing.Significant post-seismic gravity changes are detected by GRACE also,which shows that gravity rises on both sides of the seismic rupture.However,the rate of gravity change is faster on the ocean side.Here we combine the theories of afterslip and viscoelastic dislocation to simulate the post-seismic deformations and explore the comprehensive application of GPS and GRACE observations.The results demonstrate the combination of afterslip and viscoelastic relaxation
theories can make a reasonable explanation for the post-seismic deformations of the MW9.0 Tohoku-Oki earthquake.The contribution of afterslip plays a major role in the initial stage,and it gradually weakens one or two years later,while the contribution of viscoelastic relaxation increases with time.The method of combining GPS and GRACE observations is formed in the simulation.Firstly,determine a preliminary regional viscous structure by inversion of post-seismic GPS observation,then modify the viscosity of the deepest layer according to GRACE observation,and fine tune the viscosity of the shallower layer by synthetically using GPS and GRACE observations.Finally,determine the regional viscous structure.Based on this method,we estimated the mantle viscous structure in the region of the MW9.0 Tohoku-Oki earthquake by GPS and GRACE observations.The simulation results show that the rheological parameters are different on the two sides of the fault.The viscosity of the top mantle on the continental side is of the order of 1.0×1019Pa·s,while that on the ocean side is of the order of 6.0×1018Pa·s.%利用GPS和GRACE观测数据研究了日本MW9.0 地震的震后变形特征.GPS观测显示,区域震后位移呈现随指数函数变化特征,变化速率符合大森公式的衰减特性;近五年的震后水平位移累积已达到东向60～165 cm,南向20～65 cm的量值,距震中较远站点已超过同震变化量,且震后变形仍然持
续.GRACE 观测到显著的震后重力变化,地震破裂两侧的重力变化总体均呈上升趋势,但海洋侧的变化速率较快.联合震后余滑和黏弹性位错理论对震后变形进行了模拟,探索了GPS和GRACE观测的综合应用方法.研究发现,综合考虑震后余滑和黏滞性松弛效应可以对日本地震的震后变形做出较合理的解释,震后初期余滑起主要作用,1 至2 年以后逐渐减弱,黏滞性松弛作用逐渐增强.在震后变形模拟和区域黏滞性
结构反演中形成GPS和GRACE观测结合应用的方法,先基于震后GPS形变估算区域黏滞性结构,而后利用GRACE观测修正深部的黏滞系数,并综合利用这两种观测微调浅层黏滞系数,最终确定区域黏滞性结构.基于该方法反演了日本震源区的地幔黏滞性结构,地震断层破裂两侧的流变参数存在差异,大陆侧的地幔顶层黏滞系数在1.0×1019Pa·s量级,而海洋侧的则略小于大陆的,在6.0×1018Pa·s量级.
【总页数】14页(P2691-2704)
【作者】梁明;王武星;张晶
【作者单位】中国地震局地震预测重点实验室(中国地震局地震预测研究所),北京100036;广东省地震局,广州 510070;中国地震局地震预测重点实验室(中国地震局地震预测研究所),北京 100036;中国地震局地震预测重点实验室(中国地震局地震预测研究所),北京 100036
【正文语种】中文
【中图分类】P228;P315
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