2011年日本MW9.0地震对沂沭断裂带及其两侧地区地壳运动的同震影响研究

Coseismic effects of the Tohoku MW9.0 earthquake in 2011 on the crustal movement of Yishu fault zone and its bilateral areas

2011年日本MW9.0地震(简称日本地震)后沂沭断裂带及其两侧地区地震活动显著增强,研究日本地震对该地区地壳运动及地震潜势的影响十分必要.为此,本文通过112个连续GPS观测站获取了研究区高空间分辨率的日本地震同震形变场并得到如下认识:(1)8个定点地球物理观测的同震响应验证了本文同震形变场的可靠性;日本地震的东向拉张使研究区整体上处于张性同震应变状态,但存在局部挤压区域,其中莱州湾至海州湾的挤压条带穿过沂沭断裂带并对断裂带南北两段产生了不同的同震作用,对南段具有拉张作用,对北段产生挤压作用;(2)同震形变场在鲁东隆起和鲁西断块产生了显著的剪应变,地震b值显示上述区域的构造应力在日本地震后增强,因此同震形变场可能改变了这些区域的应力特征;(3)地震矩张量叠加分析显示,同震形变场短期内对鲁西断块、鲁东隆起区和沂沭断裂带南段累积了地震矩,可能有助于上述区域在日本地震以后的地震活动增强;日本地震对沂沭断裂带北段的地震矩具有释放作用,或许是该区域地震活动减弱的原因.

After the Tohoku M W9.0 earthquake in 2011,the seismic activity in Yishu fault zone and its bilateral areas increased significantly,it is necessary to study the influence of the M W9.0 earthquake on crustal movement and earthquake potential in this area.Therefore,coseismic deformation field of the M W9.0 earthquake with high spatial resolution was obtained through 112 continuous GPS observation stations in the study area and the following understanding was revealed:(1)Coseismic response of 8 fixed-point geophysical observations verified the reliability of the coseismic deformation field in this paper;Eastern extension by the M W9.0 earthquake lead to the study area a state of extensional coseismic strain on the whole,but there was still some compression region there.The compression strip from Laizhou bay to Haizhou bay passed through the Yishu fault zone and had different coseismic effects on north and south sections of the fault zone,with a tensile effect on south section and a compressive effect on north section.(2)The coseismic deformation field produced significant shear strain in East Shandong uplift and West Shandong fault block,and seismic b-value showed that tectonic stress there increased after the M W9.0 earthquake,so the coseismic deformation field may have changed the stress characteristics of these areas;(3)Seismic moment tensor overlay analysis shows that the coseismic deformation field has accumulated seismic moments on West Shandong fault block,East Shandong uplift and south section of Yishu fault zone in a short period of time,which may help to accelerate the release of seismic activity after the M W9.0 earthquake in the above areas;Meanwhile the M W9.0 earthquake released the seismic moment in north section of Yishu fault zone,which may be reason for the weakening of seismic activity in this area.