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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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。
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.
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.
引文
[1]焦青,杨选辉,许丽卿,等.汶川8.0级地震前后龙门山断裂活动特征浅析[J].大地测量与地球动力学,2008,28(4):7-11.
[2]王曰风,刁桂苓,张秀萍,等.2001年云南永胜6.0级地震余震序列震源机制解与震源应力场分析[J].地震研究,2008,31(2):119-122.
[3]许向彤,许忠淮,张东宁,等.1995求震源机制解P波初动解的格点尝试概率法[J].地震地磁观测与研究,1995,16(4):34-42.
[4]许忠淮,汪素云,高阿甲,等.我国部分早期震源机制解答的中心测定[J].地震地磁观测与研究,1994,15(5):1-9.
[5]许忠淮,阎明,赵仲和.由多个小地震推断的华北地区构造应力场的方向[J].地震学报,1983,5(3):268-279.
[6]程万正,阮祥,张永久.川滇次极地块震源机制解类型与一致性参数[J].地震学报,2006,28(6):561-573.
[7]胡幸平,俞春泉,陶开,等.利用P波初动资料求解汶川地震及其余震震源机制解[J].地球物理学报,2008,51(6):1 711-1 718.
[8]焦青,杨选辉,许丽卿,等.汶川8.0级地震前后龙门山断裂活动特征浅析[J].大地测量与地球动力学,2008,28(4):7-11.
[9]刘超,张勇,许力生,等.一种矩张量反演新方法及其对2008年汶川MS8.0地震序列的应用[J].地震学报,2008,30(4):329-339.
[10]龙海英,聂晓红,高国英.新疆天山地区与川滇地区中强地震震源机制解对比分析[J].地震研究,2007,30(3):229-234.
[11]屠泓为,都昌庭,马震,等.利用P波初动计算青海中强地震的震源机制解[J].高原地震,2008,20(1):22-26.
[12]许力生,蒋长胜,陈运泰,等.2004年首都圈地区中小地震的矩张量反演[J].地震学报,2007,29(3):229-239.
[13]许忠淮.地震参数-数字地震学在地预测中的应用[M].北京:地震出版社,2003.16-25.
[14]杨中书,李超.利用P波初动及振幅比初步计算2005年11月26日九江-瑞昌地震余震序列震源机制[J].华南地震,2006,26(3):77-82.
[15]周翠英,华爱军,蒋海昆,等.以格点尝试法求取得山东地区现代中小地震震源机制解[J].东北地震研究,2003,19(1):1-11.
[16]张萍,谷光裕,高艳玲.岫岩-海城MS5.4级地震序列震源机制解[J].地震,2001,21(1):98-102.
[17]张萍,蒋秀琴.岫岩-海城MS5.4地震序列的震源机制解及应力场特征[J].地震地磁观测与研究,2001,22(2):76-82.
[18]张萍,于龙伟,李涯,等.岫岩-海城MS5.4地震前小震震源机制解与记录特征分析[J].地震地磁观测与研究,2003,24(1):29-38.
[19]周云好,许力生,陈运泰.2000年6月4日印度尼西亚苏门答腊南部MS8.0地震的震源机制[J].地震学报,2002,24(5):462-469.
[20]A R.Banghar.Focal Mechanism Of Indian Earthquakes[J].BSSA,1972,62(2):603-608.
[21]R S CROSSON,E T ENDO R S Crosson.Focal Mechanisms of Earthquakes Related to the 29 No-vember 1975 Kalapana,Hawaii,Earthquak:the Effect of Structure Models[J].BSSA,1981,71(3):713-729.
[22]Yih-Min Wu,Li Zhao,Chien-Hsin Chang,et al.Focal-Mechanism Determination in Taiwan by Ge-netic Algorithm[J].BSSA,2008,98(2):651-661.
[23]黄媛,吴建平,张天中,等.汶川8.0级大地震及其余震序列重定位研究[J].中国科学D辑,2008,38(5):1 242-1 249.
①http://www.ceic.ac.cn/ceic/subjects/20080512142804/20080512142804_CMT.jsp
②http://www.globalcmt.org/CMTfiles.ht ml
③http://neic.usgs.gov/neis/sopar/
④http://www.cea-igp.ac.cn/共享资源/汶川地震余震序列震源机制解/01.pdf
[2]王曰风,刁桂苓,张秀萍,等.2001年云南永胜6.0级地震余震序列震源机制解与震源应力场分析[J].地震研究,2008,31(2):119-122.
[3]许向彤,许忠淮,张东宁,等.1995求震源机制解P波初动解的格点尝试概率法[J].地震地磁观测与研究,1995,16(4):34-42.
[4]许忠淮,汪素云,高阿甲,等.我国部分早期震源机制解答的中心测定[J].地震地磁观测与研究,1994,15(5):1-9.
[5]许忠淮,阎明,赵仲和.由多个小地震推断的华北地区构造应力场的方向[J].地震学报,1983,5(3):268-279.
[6]程万正,阮祥,张永久.川滇次极地块震源机制解类型与一致性参数[J].地震学报,2006,28(6):561-573.
[7]胡幸平,俞春泉,陶开,等.利用P波初动资料求解汶川地震及其余震震源机制解[J].地球物理学报,2008,51(6):1 711-1 718.
[8]焦青,杨选辉,许丽卿,等.汶川8.0级地震前后龙门山断裂活动特征浅析[J].大地测量与地球动力学,2008,28(4):7-11.
[9]刘超,张勇,许力生,等.一种矩张量反演新方法及其对2008年汶川MS8.0地震序列的应用[J].地震学报,2008,30(4):329-339.
[10]龙海英,聂晓红,高国英.新疆天山地区与川滇地区中强地震震源机制解对比分析[J].地震研究,2007,30(3):229-234.
[11]屠泓为,都昌庭,马震,等.利用P波初动计算青海中强地震的震源机制解[J].高原地震,2008,20(1):22-26.
[12]许力生,蒋长胜,陈运泰,等.2004年首都圈地区中小地震的矩张量反演[J].地震学报,2007,29(3):229-239.
[13]许忠淮.地震参数-数字地震学在地预测中的应用[M].北京:地震出版社,2003.16-25.
[14]杨中书,李超.利用P波初动及振幅比初步计算2005年11月26日九江-瑞昌地震余震序列震源机制[J].华南地震,2006,26(3):77-82.
[15]周翠英,华爱军,蒋海昆,等.以格点尝试法求取得山东地区现代中小地震震源机制解[J].东北地震研究,2003,19(1):1-11.
[16]张萍,谷光裕,高艳玲.岫岩-海城MS5.4级地震序列震源机制解[J].地震,2001,21(1):98-102.
[17]张萍,蒋秀琴.岫岩-海城MS5.4地震序列的震源机制解及应力场特征[J].地震地磁观测与研究,2001,22(2):76-82.
[18]张萍,于龙伟,李涯,等.岫岩-海城MS5.4地震前小震震源机制解与记录特征分析[J].地震地磁观测与研究,2003,24(1):29-38.
[19]周云好,许力生,陈运泰.2000年6月4日印度尼西亚苏门答腊南部MS8.0地震的震源机制[J].地震学报,2002,24(5):462-469.
[20]A R.Banghar.Focal Mechanism Of Indian Earthquakes[J].BSSA,1972,62(2):603-608.
[21]R S CROSSON,E T ENDO R S Crosson.Focal Mechanisms of Earthquakes Related to the 29 No-vember 1975 Kalapana,Hawaii,Earthquak:the Effect of Structure Models[J].BSSA,1981,71(3):713-729.
[22]Yih-Min Wu,Li Zhao,Chien-Hsin Chang,et al.Focal-Mechanism Determination in Taiwan by Ge-netic Algorithm[J].BSSA,2008,98(2):651-661.
[23]黄媛,吴建平,张天中,等.汶川8.0级大地震及其余震序列重定位研究[J].中国科学D辑,2008,38(5):1 242-1 249.
①http://www.ceic.ac.cn/ceic/subjects/20080512142804/20080512142804_CMT.jsp
②http://www.globalcmt.org/CMTfiles.ht ml
③http://neic.usgs.gov/neis/sopar/
④http://www.cea-igp.ac.cn/共享资源/汶川地震余震序列震源机制解/01.pdf
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