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利用CAP法研究重庆荣昌2014年2月23日ML3.8地震震源机制
王小龙1 雷兴林2 郭欣1 于天航1 勾宪斌1 余国政1
1.重庆市地震局,重庆,401137;2.日本地质调查所,筑波,305-8567
摘要:
利用CAP(cut-and-paste)法反演2014年2月23日重庆荣昌ML3.8地震震源机制,得到震级MW为3.04,节面Ⅰ走向46°、倾角44°、滑动角74°,节面Ⅱ走向247°、倾角48°、滑动角104°,P轴方位147.25°、仰角-2.09°,T轴方位46°、仰角-78.76°,表明该地震是带走滑分量的逆冲型地震。CAP测定的这次ML3.8震源深度为3km,在盖层内,震源机制解中节面Ⅱ走向、倾角与震中附近的一条深度为1700m走向为SW230°倾向NW,倾角约45°的“腹底”逆断层基本一致。震中位于荣昌天然气田,附近有几口废水回注深井,曾发生大量的注水诱发地震。本次地震亦有可能是在区域主应力场的作用下,注水后岩石的孔隙发生变化触发了盖层内“腹底”断层活动的结果。
关键词:  荣昌地震  CAP方法  震源机制
DOI:
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Focal Mechanism Solution of the February 23,2014,ML3. 8 Rongchang Earthquake with the CAP (Cut and Paste) Method
Wang Xiaolong1),Lei Xinglin2),Guo Xing1),Yu Tianhang1),Gou Xianbin1),and Yu Gouzheng1)
1) Earthquake Administration of Chongqing Municipality,Chongqing 401147,China;2) Geological Survey of Japan,AIST,Tsukuba 305-8567,Japan
Abstract:
A ML 3. 8 earthquake occurred on February 23,2014 in Rongchang County,which is located at the southern edge of the Sichuan Basin in the border area between Sichuan and Chongqing. This paper presents results of focal mechanism solution of this earthquake using the CAP ( cut and paste) method based on broadband seismograms recorded by regional seismic stations. Our results show that the moment magnitude is MW 3. 09 and focal depth is 3km. The hypocenter of this earthquake is located close to a buried fault in the Luoguangshan anticline. Oil prospecting and deep drilling data indicate that this buried fault is a thrust fault,striking SW230°,dipping NW45°,and 1. 7km deep. There are some injection wells within the anticline,and significant injection-induced earthquakes were observed during the periods of injection of waste water into the deep formations through those wells. The best double couple solution of the ML3. 8 earthquake is 247°,48° and 104° for strike,dip and rate,respectively,for one nodal plane (and 46°,44° and 74° for another nodal plane),which is in agreement with the geometry of the buried fault. Therefore,we conclude that the ML 3. 8 Rongchang earthquake is possibly the result of faulting along the buried reverse fault induced by water injection under the compressive stress regime in the area.
Key words:  Rongchang earthquake  Cut and Paste method  Focal mechanism  Injection-induced earthquake