| 龙门山断裂带多参数深部结构成像与地震成因研究 |
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| 引用本文： | 王志,王绪本,黄润秋,刘冠男.龙门山断裂带多参数深部结构成像与地震成因研究[J].地球物理学报,2017,60(6):2068-2079. |
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| 作者姓名： | 王志 王绪本 黄润秋 刘冠男 |
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| 作者单位： | 1. 中国科学院南海海洋研究所边缘海和大洋地质重点实验室, 广州 510301;2. 成都理工大学地球探测与信息技术教育部重点实验室, 成都 610059;3. 成都理工大学地质灾害防治与地质环境保护国家重点实验室, 成都 610059 |
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| 基金项目： | 国家自然科学基金（41372229，41572201），中国科学院百人计划（17314059）及地质灾害防治与地质环境保护国家重点实验室开放基金（SKLGP2016K016）资助. |
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| 摘 要： | 通过反演大量的纵、横波地震数据,获得了沿龙门山断裂带及周边区域的深部三维精细结构,结合前人二维大地电磁探测研究成果,提出龙门山断裂带地壳形变与深部速度结构和导电率不均匀性有关,探讨了2008年汶川和2013年芦山地震的诱发和产生与流体侵入及地壳形变的密切关系.本研究发现,2008年汶川地震发生在高速度、高泊松比和低电导率的区域,2013年芦山地震则位于高速度、低泊松比和低电导率的发震层.在上地壳中,四川前陆盆地的低速、低泊松比和低阻异常与松潘一甘孜地块的高速、高泊松比和高阻异常形成了鲜明的对比.在龙门山断裂带下方的两个低速和低阻块体,将龙门山断裂带分成南、中和北三段.我们的研究认为,这两个异常体与来自松潘甘孜地块的下地壳和(或)上地幔的局部熔融或流体侵入到龙门山断裂带的脆弱区有关.基于对汶川和芦山地震的余震分布特征及震源区的地震波速度、泊松比及电阻率参数分析,揭示了龙门山断裂带深部剧烈的地壳形变与流体应力积累对2008年汶川和2013年芦山地震的触发及其地震破裂过程具有重要的控制作用.
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| 关 键 词： | 地壳形变 龙门山断裂带 地震成因 下地壳流 深部结构成像 |
| 收稿时间： | 2016-09-26 |
Deep structure imaging of multi-geophysical parameters and seismogenesis in the Longmenshan fault zone |
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| WANG Zhi,WANG Xu-Ben,HUANG Run-Qiu,LIU Guan-Nan.Deep structure imaging of multi-geophysical parameters and seismogenesis in the Longmenshan fault zone[J].Chinese Journal of Geophysics,2017,60(6):2068-2079. |
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| Authors: | WANG Zhi WANG Xu-Ben HUANG Run-Qiu LIU Guan-Nan |
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| Institution: | 1. CAS Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;2. Key Laboratory of Earth Exploration and Information Techniques of Ministry of Education, Chengdu University of Technology, Chengdu 610059, China;3. State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China |
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| Abstract: | Deep structures of seismic velocity and Poisson's ratio are imaged along the Longmenshan fault zone using a large number of arrival-time data of P- and S-waves. Together with magnetotelluric (MT) data analyzing, we consider that the crustal deformation is closely related to the deep seismic velocity, Poisson's ratio and conductivity structural heterogeneities. The generations of the 2008 Wenchuan and 2013 Lushan earthquakes are associated with the crustal deformation process and fluid intrusion from the lower crust of Tibet into the seismogenic layer along the fault zone. Our results indicate that the 2008 Wenchuan and 2013 Lushan earthquakes are located in the high velocity and high resistivity zones within the seismogenic layer. Anomalously slow velocity with low resistivity in the Sichuan foreland basin is in sharp contrast to high-velocity and high-resistivity anomalies in the upper crust in the Songpan-Garzê block. This contrasting feature of the anomalies could reflect the Mesozoic and Paleozoic sediments with thickness variation of several kilometers to more than 10 kilometers in the Sichuan Basin. The tomographic model presented here reveals two crustal bodies with anomalously slow velocity and high conductivity underneath the Longmenshan fault zone which is separated into three contrasting segments by the two bodies. We interpreted these low-velocity and low-resistivity bodies as being associated with extrusion of either fluids or products of partial melting from the lower crust, the upper mantle, or both in the Songpan-Garzê block, which suggests strong variations in the rheological strength of the rock along the fault zone. This finding implies that the coupling between these presumably fluid-bearing bodies and earthquake generation could be extremely complex and that there is dramatic variation from the southwestern portion to the northeastern segment along the fault belt. We then conclude that the 2008 Wenchuan earthquake generation as well as its rupture process is controlled by the structural heterogeneities together with the fluids intruding from the lower crust of the central plateau. The 2013 Lushan earthquake might have been triggered by the high pore-pressure accumulated in source area from both the lower crustal fluids intrusion and the stress transmission of the 2008 Wenchuan earthquake in the seismogenic layer. Our study suggests that the rheological variation in the crust and fluids bearing stress accumulation along the Longmenshan fault zone played a principal role in controlling seismic generation and rupture processes during the 2008 Wenchuan and 2013 Lushan earthquakes. |
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| Keywords: | Crustal deformation Longmenshan fault zone Seismogenesis Fluid intrusion Deep structural imaging |
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