Focal Mechanism Solutions for the 2008 MS8.0 Wenchuan Earthquake and Part of its Aftershocks
Focal Mechanism Solutions for the 2008 MS8.0 Wenchuan Earthquake and Part of its Aftershocks
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发表时间：
2010
影响因子：
3
通讯作者：
Li Yan’e
中科院分区：
文献类型：
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作者：
Li Yan’e
本文确定了2008年5月12日汶川地震的震源机制解利用等面积投影图解法和区域台及远台Pn、Pg波初动符号资料，对2008年12月10日前四川发生的10次MS8.0地震及其部分余震进行了分析，得到汶川MS8.0地震震源机制解为：节点Ⅰ：走向5°，倾角48°，滑动角39°：结点Ⅱ：走向247°，倾角62°，滑动角131°; P轴方位角309°，倾伏8°，T轴方位角208°，倾伏54°，B轴方位角44°，倾伏35°。结合地质和余震空间分布，Ⅱ节为发震断层，触发大地震的断层活动为逆冲推覆，S67°W的主破裂面与北51 °西主压应力P轴与区域构造应力场方向基本一致。龙门山断裂带南、北方两段余震具有明显的优势方位，且有明显的差异，南部早期余震断裂以逆倾滑动为主，兼有走滑，北部晚期余震断裂以走滑为主，兼有逆倾滑动，南部应力场受主震应力场控制，北部应力场受主震应力场和区域应力场共同控制。
This paper determines the focal mechanism solutions for the May 12,2008 Wenchuan earthquakes(MS8.0) occured 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 MS8.0 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.