| 2008年5月12日四川汶川8.0级地震与部分余震的震源机制解 |
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| 引用本文： | 郭祥云,陈学忠,李艳娥.2008年5月12日四川汶川8.0级地震与部分余震的震源机制解[J].地震,2010,30(1). |
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| 作者姓名： | 郭祥云 陈学忠 李艳娥 |
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| 作者单位： | 中国地震局地球物理研究所,北京,100081 |
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| 基金项目： | 中国地震局地球物理研究所基本业务专项(DQJB08B17)资助 |
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| 摘 要： | 采用区域和远台Pn或Pg初至波初动符号,利用下半球等面积投影,求解了2008年5月12日四川汶川8.0级地震和截止到2008年12月10日发生的部分4级以上余震的震源机制解。汶川8.0级地震的震源机制为:节面Ⅰ的走向为5°,倾角为48°,滑动角为39°;节面Ⅱ的走向为247°,倾角为62°,滑动角为131°。P轴方位角为309°,仰角为8°,T轴方位角为208°,仰角为54°,B轴方位角为44°,仰角为35°。结合地质构造和余震空间分布,可以确定节面Ⅱ为发震断层面。根据震源机制解,引发本次地震的断层活动主要表现为逆冲,主破裂面为S67°W与该地震所在断层的走向基本一致(断裂总体走向N45°E)1];主压应力轴P轴为N51°W,主压应力轴P轴方位与该区域构造应力场方向基本一致。根据余震震源机制解结果,龙门山断裂带南段发生的余震与北段发生的余震的震源机制都具有优势分布,且两者差异明显。早期发生在南段的余震的破裂是以逆倾滑动为主,兼有走向滑动;而随着时间的推移,余震向北段迁移,在龙门山构造的北段地震震源的破裂方式以走向滑动为主,兼有一定的逆倾滑动;龙门构造带南段震源应力场受主震应力场的控制,而龙门构造带北段震源应力场不仅受区域应力场的影响,还受主震应力场的影响。
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| 关 键 词： | 初动符号 汶川地震序列 震源机制 |
Focal Mechanism Solutions for the 2008 M_S8.0 Wenchuan Earthquake and Part of its Aftershocks |
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| GUO Xiang-yun,CHEN Xue-zhong,LI Yan-e.Focal Mechanism Solutions for the 2008 M_S8.0 Wenchuan Earthquake and Part of its Aftershocks[J].Earthquake,2010,30(1). |
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| Authors: | GUO Xiang-yun CHEN Xue-zhong LI Yan-e |
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| Institution: | Institute of Geophysics;CEA;Beijing 100081;China |
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| Abstract: | This paper determines the focal mechanism solutions for the May 12, 2008 Wenchuan earthquakes (M_S8.0) occurred in Sichuan province and part of its aftershocks up to Dec 10, 2008 using graphical interpretation of equal area projection and the first motion sign data of Pn and Pg waves from regional and distant stations. The focal mechanism solution of the Wenchuan M_S8.0 earthquakes is: Nodal Ⅰ: strike 5°, dip angle 48°, slip angle 39°; Nodal Ⅱ: strike 247°, dip angle 62°, slip angle 131°; P axis azimuth 309°, plunge 8°, T axis Azimuth 208°, plunge 54°, B axis Azimuth 44°, plunge 35°. Combining geology and spatial distribution of aftershocks, nodal II can be identified as the seismogenic fault. The faulting activities triggering the huge earthquake is reverse thrusting. The main fracture surface of S67°W is basically the same as the fault strike. The main compression stress P axis of N51°W is basically the same as the direction of regional tectonic stress field. Aftershocks occurred in the southern and northern section of the Longmenshan fault zone have the predominant orientations, and are obviously different. Early aftershock faultings in the south are mainly characterized maily by reverse-dip slip, with some strike-slip. Later faultings in the north are characterized mainly by strike-slip, with some reverse-dip slip. Stress field in the south is controlled by the main earthquake stress field, while stress field in the north is controlled by both the main earthquake stress filed and regional stress field. |
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| Keywords: | First motion sign data Wenchuan earthquake Focal mechanism |
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