东昆仑断裂带东端和2017年九寨沟7.0级地震区深部电性结构探测  

ELECTRICAL STRUCTURE OF THE 2017 MS7.0 JIUZHAIGOU EARTHQUAKE REGION AND THE EASTERN TERMINUS OF THE EAST KUNLUN FAULT

作　　者：孙翔宇[1] 詹艳[1] 赵凌强 陈小斌[1] 李陈侠[3] 孙建宝[1] 韩静 崔腾发 SUN Xiang-yu;ZHAN Yan;ZHAO Ling-qiang;CHEN Xiao-bin;LI Chen-xia;SUN Jian-bao;HAN Jing;CUI Teng-fa(State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China;The Second Monitoring and Application Center,China Earthquake Administration,Xi′an 710043,China;Shaanxi Earthquake Agency,Xi′an 710068,China)

机构地区：[1]中国地震局地质研究所,地震动力学国家重点实验室,北京100029 [2]中国地震局第二监测中心,西安710043 [3]陕西省地震局,西安710068

出　　处：《地震地质》2020年第1期182-197,共16页Seismology and Geology

基　　金：国家自然科学基金(41474057);中国地震局九寨沟地震科考项目;中国地震局地震行业科研专项(20130811)共同资助.

摘　　要：东昆仑断裂带是青藏高原北部一条近EW走向的巨型断裂,其东南尾端发生分叉形成了复杂的马尾状断裂系统,2017年在该区域发生了九寨沟M_S7.0地震。文中对跨过东昆仑断裂带东端和九寨沟地震区的3条剖面上的大地电磁探测数据进行处理分析,采用三维电磁成像反演技术获取了三维深部电性结构图像。所得结果表明,东昆仑断裂带东端及周边区域内的东昆仑断裂、白龙江断裂和光盖山-迭山断裂表现出向SW倾斜的电性差异带,这些断裂向下延伸并合并于中下地壳的低阻层中,共同组成了由南向北扩展的花状构造。在马尾状构造中,隐伏的虎牙断裂带(北段)在深部表现为明显的低阻边界带;塔藏断裂的规模明显小于虎牙断裂(北段),并与虎牙断裂(北段)组成单侧花状结构;白龙江断裂和光盖山-迭山断裂依然表现为由南向北扩展的花状构造,2组花状结构在深部衔接并统一归并于壳内的低阻层中。2017年九寨沟7.0级地震的震源区位于高、低阻交界区域,处于松潘-甘孜地块壳内低阻层向NE涌动的端点附近,根据震源区的电性结构和流变结构推测震源深度≤11km。虎牙断裂(北段)的延伸深度和规模大于东侧的塔藏断裂,是2017年九寨沟地震的发震断层。松潘-甘孜地块北部中下地壳发育南西深、北东浅的低阻层,表明青藏高原向NE推挤的运动方式是2017年九寨沟地震的动力来源。The East Kunlun Fault is a giant fault in northern Tibetan,extending eastward and a boundary between the Songpan-Ganzi block and the West Qinling orogenic zone.The East Kunlun Fault branches out into a horsetail structure which is formed by several branch faults.The 2017 Jiuzhaigou MS7.0 earthquake occurred in the horsetail structure of the East Kunlun Fault and caused huge casualties.As one of several major faults that regulate the expansion of the Tibetan plateau,the complexity of the deep extension geometry of the East Kunlun Fault has also attracted a large number of geophysical exploration studies in this area,but only a few are across the Jiuzhaigou earthquake region.Changes in pressure or slip caused by the fluid can cause changes in fault activity.The presence of fluid can cause the conductivity of the rock mass inside the fault zone to increase significantly.MT method is the most sensitive geophysical method to reflect the conductivity of the rock mass.Thus MT is often used to study the segmented structure of active fault zones.In recent years MT exploration has been carried out in several earthquake regions and the results suggest that the location of main shock and aftershocks are controlled by the resistivity structure.In order to study the deep extension characteristics of the East Kunlun Fault and the distribution of the medium properties within the fault zone,we carried out a MT exploration study across the Tazang section of the East Kunlun Fault in 2016.The profile in this study crosses the Jiuzhaigou earthquake region.Other two MT profiles that cross the Maqu section of East Kunlun Fault performed by previous researches are also collected.Phase tensor decomposition is used in this paper to analyze the dimensionality and the change in resistivity with depth.The structure of Songpan-Ganzi block is simple from deep to shallow.The structure of West Qinlin orogenic zone is complex in the east and simple in the west.The structure near the East Kunlun Fault is complex.We use 3 D inversion to image the t

关 键 词：孕震环境 2017年九寨沟M_S7.0地震 大地电磁三维成像 昆仑-秦岭断裂系 

分 类 号：P315.722[天文地球—地震学]