CAP方法反演新丰江锡场地区ML4.0级以上地震震源机制解

Focal Mechanism Inversion of M_L≥4.0 Earthquakes in Xichang, Xinfengjiang Reservoir by CAP Method

利用区域台网宽频带波形数据,采用CAP方法反演了锡场地区5次M_L4.0级以上地震的震源机制解,并结合地震精定位和区域活动构造讨论了其发震构造。结果显示:2012年2月16日M_L5.2级地震的震源机制解为,节面Ⅰ:走向351°、倾角84°、滑动角-23°,节面Ⅱ:走向83°、倾角67°、滑动角-173°,最佳震源深度10.39 km; 2013年2月22日M_L5.1级地震的震源机制解为,节面Ⅰ:走向274°、倾角55°、滑动角-118°,节面Ⅱ:走向136°、倾角43°、滑动角-56°,最佳震源深度10.88 km。其它3个事件均以走滑为主,破裂类型与M_L5.2级地震相似。最佳拟合震源深度集中在上地壳底部的8 km和10 km。结合区域构造和地震序列精定位结果,认为2014年7月11日M_L4.5级地震NW向的节面Ⅰ为真实破裂面, 2012年的2次地震和2014年4月25日M_L4.4级地震NEE向的节面Ⅱ为真实破裂面, 2013年2月22日M_L5.1级地震真实破裂面是近EW向的节面Ⅰ, 2012年2次地震和2014年4月的1次地震活动可能与近EW走向的大坑南断裂有关,锡场地区可能存在多条相互交割的隐伏断裂。

Using regional broadband waveform data,the paper inversed the focal mechanisms of five ML≥4.0 earthquakes swarmed in Xichang,Xinfengjiang reservoir by CAP method,and discussed the seismogenic fault based on the relocated events and regional active fault data. The results show that the best CMT solution of the Feb 16th 2012 ML 5.2 earthquake is,Plane I： strike=351°,dip=84° and rake=-23°,plane II：strike=83°,dip=67° and rake=-173°,and the best fitting depth is 10.39 km. The best CMT solution of the Feb 22nd 2013 ML 5.1 earthquake is,Plane I：strike=274°,dip=55° and rake=-118°,plane II： strike=136°,dip=43° and rake=-56°,and the best fitting depth is 10.88 km. The focal mechanisms of other three earthquakes are consistent with the ML 5.2 earthquake,typically strike slip fault. And the best fitting depth are concentrated on 8km and 10 km, which located in the lower part of the upper crust. By analyzing the relocated earthquake distributions and regional active fault,the paper consider the true slip fault of the two earthquakes in 2012 and the one earthquake in Ape 25th 2014 is NEE trending nodal plane Ⅰ. And EW trending nodal plane Ⅱ is the Feb 22nd 2013 ML 5.1 earthquake＇s truth slip fault. The EW trending Dakeng south active fault may be the active fault of the two earthquakes in 2012 and the one earthquake in Feb 2014. Some crossing buried faults may exist in the Xichang area.