| Fault plane solutions in Sichuan-Yunnan rhombic block and their dynamic implications |
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| 作者姓名： | 刘平江 刁桂苓 宁杰远 |
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| 作者单位： | School of Earth and Space Sciences Peking University，Earthquake Administration of Hebei Province，School of Earth and Space Sciences Peking University，Beijing 100871 China，Shijiazhuang 050021 China，Beijing 100871 China |
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| 基金项目： | State Key Basic research and Development Project from Ministry of Science and Technology of China （2004cb418406） and National Natural Science Foundation of China （40521002）. Acknowledgments We thank Professor YIN Xiang chu, WU Zhong liang, ZHANG Dong ning, CUI Xiao feng, CHEN Lian wang, as well as Mr. WEI Rong qiang, WANG Shu guang, L0U Xiao ting for helpful discussions. And we also appreciate the comments and suggestions of two anonymous reviewers. |
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| 摘 要： | Harvard Centroid Moment Tensor (CMT) solutions for earthquakes from 1977 to 2004 showed that the stress fields are obviously different in northwestern Sichuan sub-block (NWSSB), western parts of Central Yunnan sub-block (CYSB) and eastern part of CYSB. The characteristics of the mean stress fields in these three regions are obtained by fitting to CMT solutions. The stress state in NWSSB is characterized by its sub-horizontal tensile principal axis of stress (T axis) in roughly N-S direction and west dipping compressive principal axis of stress (P axis); the one in western part of CYSB is characterized by its ENE dipping T axis and sub-horizontal medium prin-cipal axis of stress (B axis) in roughly N-S direction; the one in eastern part of CYSB is characterized by its sub-horizontal P axis in roughly NNW-SSE direction and sub-horizontal T axis in roughly WSW-ENE direction. Finite element method simulation clearly shows that the Indian Plate imposes great extrusion on Sichuan-Yunnan rhombic block (SYRB) near Assam massif. The value of the simulated compressive principal stress decreases with the distance from Assam massif. The simulated directions of the T axes in SYRB form annular distribution encir-cling Assam. For a homogeneous elastic medium with free boundary conditions on the top and bottom surfaces as well as the displacement boundary conditions derived from the GPS observations on the lateral boundaries, the computation results are consistent with the Harvard CMT solutions in NWSSB and western part of CYSB, while inconsistent with the Harvard CMT solutions in eastern part of CYSB. The inconsistency in eastern part of CYSB can be reduced when it includes inhomogeneous elastic media. The stress states in NWSSB and western part of CYSB revealed by the Harvard CMT solutions are not local, which are mainly controlled by the boundary force on the whole region. On the other hand, the stress state in eastern part of CYSB given by the Harvard CMT solutions is local, which may be affected by local topography, material inhomogeneity, and the drag force underneath.
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| 关 键 词： | 中国 四川 云南 交界区域 地震 发生原因 |
| 文章编号： | 1000-9116（2007）05-0479-10 |
| 收稿时间： | 23 May 2007 |
| 修稿时间： | 2007-05-23 |
Fault plane solutions in Sichuan-Yunnan rhombic block and their dynamic implications |
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| Liu Ping-jiang , Diao Gui-ling and Ning Jie-yuan.Fault plane solutions in Sichuan-Yunnan rhombic block and their dynamic implications[J].Acta Seismologica Sinica(English Edition),2007,20(5):479-488. |
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| Authors: | Liu Ping-jiang Diao Gui-ling and Ning Jie-yuan |
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| Institution: | 1. School of Earth and Space Sciences, Peking University, Beijing 100871, China; 2. Earthquake Administration of Hebei Province, Shijiazhuang 050021, China |
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| Abstract: | Harvard Centroid Moment Tensor (CMT) solutions for earthquakes from 1977 to 2004 showed that the stress fields are obviously different in northwestern Sichuan sub-block (NWSSB), western parts of Central Yunnan sub-block (CYSB) and eastern part of CYSB. The characteristics of the mean stress fields in these three regions are obtained by fitting to CMT solutions. The stress state in NWSSB is characterized by its sub-horizontal tensile principal axis of stress (T axis) in roughly N-S direction and west dipping compressive principal axis of stress (P axis); the one in western part of CYSB is characterized by its ENE dipping T axis and sub-horizontal medium prin- cipal axis of stress (B axis) in roughly N-S direction; the one in eastern part of CYSB is characterized by its sub-horizontal P axis in roughly NNW-SSE direction and sub-horizontal T axis in roughly WSW-ENE direction. Finite element method simulation clearly shows that the Indian Plate imposes great extrusion on Sichuan-Yunnan rhombic block (SYRB) near Assam massif. The value of the simulated compressive principal stress decreases with the distance from Assam massif. The simulated directions of the T axes in SYRB form annular distribution encir- cling Assam. For a homogeneous elastic medium with free boundary conditions on the top and bottom surfaces as well as the displacement boundary conditions derived from the GPS observations on the lateral boundaries, the computation results are consistent with the Harvard CMT solutions in NWSSB and western part of CYSB, while inconsistent with the Harvard CMT solutions in eastern part of CYSB. The inconsistency in eastern part of CYSB can be reduced when it includes inhomogeneous elastic media. The stress states in NWSSB and western part of CYSB revealed by the Harvard CMT solutions are not local, which are mainly controlled by the boundary force on the whole region. On the other hand, the stress state in eastern part of CYSB given by the Harvard CMT solutions is local, which may be affected by local topography, material inhomogeneity, and the drag force underneath. |
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| Keywords: | dynamics Sichuan-Yunnan rhombic block numerical simulation focal mechanism solution |
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