Deep structure beneath the southwestern section of the Longmenshan fault zone and seimogenetic context of the 4.20 Lushan M_S7.0 earthquake  

作　　者：ZHAN Yan ZHAO GuoZe UNSWORTH Martyn WANG LiFeng CHEN XiaoBin LI Tao XIAO QiBin WANG JiJun TANG Ji CAI JunTao WANG YanZhao 

机构地区：[1]State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration [2]Department of Earth and Atmospheric Sciences,University of Alberta

出　　处：《Chinese Science Bulletin》2013年第28期3467-3474,共8页

基　　金：supported by the National Basic Research Program of China(2008CB425702-2);the National Natural Science Foundation of China(41074046 and 41074047);the Director Foundation of Institute of Geology,China Earthquake Administration(IGCEA1013);the Investigation Project for Wenchuan Earthquake of China Earthquake Administration

摘　　要：Magnetotelluric measurements were carried out along two profiles across the middle and southwestern sections of the Longmenshan fault zone(LMSf)from 2009 to 2011,after the 2008 Wenchuan MW7.9 earthquake.The former profile crosses the Wenchuan event epicenter and the latter one crosses 2013 Lushan MS7.0 event epicenter.The data were analyzed using advanced processing techniques,including phase tensor and two-dimensional inversion methods,in order to obtain reliable 2-D profiles of the electrical structure in the vicinity of the two earthquakes.A comparison of the two profiles indicates both similarities and differences in the deep crustal structure of the LMSf.West of the southwestern section,a crustal high conductivity layer(HCL)is present at about 10 km depth below the Songpan-Garzêblock;this is about 10 km shallower than that under the middle section of the LMSf.A high resistivity body(HRB)is observed beneath the southwestern section,extending from the near surface to the top of upper mantle.It has a smaller size than the HRB observed below the middle section.In the middle section,there is a local area of decreased resistivity within the HRB but there is absence of this area.The 2013 Lushan earthquake occurred close to the eastern boundary of HRB and the Shuangshi-Dachuan fault,of which the seismogenic context has both common and different features in comparison with the 2008 Wenchuan event.On a large scale,the 2013 Lushan earthquake is associated with the HCL and deformation in the crust including HCL of the eastern Tibetan Plateau.In order to assess seismic risk,it is important to consider both the stress state and the detailed crustal structure in different parts of the LMSf.Magnetotelluric measurements were carried out along two profiles across the middle and southwestern sections of the Longmenshan fault zone （LMSf） from 2009 to 2011, after the 2008 Wenchuan MW7.9 earthquake. The former profile crosses the Wenchuan event epicenter and the latter one crosses 2013 Lushan MS7.0 event epicenter. The data were analyzed using advanced processing techniques, including phase tensor and two-dimensional inversion methods, in order to obtain reliable 2-D profiles of the electrical structure in the vicinity of the two earthquakes. A comparison of the two profiles indicates both similarities and differences in the deep crustal structure of the LMSf. West of the southwestern section, a crustal high conductivity layer （HCL） is present at about 10 km depth below the Songpan-Garzê block; this is about 10 km shallower than that under the middle section of the LMSf. A high resistivity body （HRB） is observed beneath the southwestern section, extending from the near surface to the top of upper mantle. It has a smaller size than the HRB observed below the middle section. In the middle section, there is a local area of decreased resistivity within the HRB but there is absence of this area. The 2013 Lushan earthquake occurred close to the eastern boundary of HRB and the Shuangshi-Dachuan fault, of which the seismogenic context has both common and different features in comparison with the 2008 Wenchuan event. On a large scale, the 2013 Lushan earthquake is associated with the HCL and deformation in the crust including HCL of the eastern Tibetan Plateau. In order to assess seismic risk, it is important to consider both the stress state and the detailed crustal structure in different parts of the LMSf.

关 键 词：龙门山断裂带 地震发生 深部结构 西南部 庐山 大地电磁测量 地壳变形 青藏高原东部 

分 类 号：P315[天文地球—地震学]