芦山7.0级地震序列的震源位置与震源机制解特征
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摘要
基于中国国家和四川区域数字地震台网记录,采用HypoDD方法精确定位了四川芦山ML2.0级以上地震序列的震源位置,采用CAP方法反演了36次ML4.0级以上地震的最佳双力偶震源机制解,并利用小震分布和区域应力场拟合了可能存在的发震断层面参数,从而综合分析了芦山地震序列的震源深度、震源机制和震源破裂面特征,探讨可能的发震构造.结果显示,7.0级主震的震源位置为30.30°N、102.97°E,初始破裂深度为15km左右,震源矩心深度为14km左右,最佳双力偶震源机制解的两组节面分别为走向209°/倾角46°/滑动角94°和走向23°/倾角44°/滑动角86°,可视为纯逆冲型地震破裂,绝大多数ML4.0级以上余震的震源机制也表现出与主震类似的逆冲破裂特征.ML2.0级以上余震序列发生在主震两侧,集中分布的长轴为30km左右,震源深度主要集中在5～27km,ML3.5级以上较大余震则集中分布在9～25km的深度上,并揭示出发震断层倾向北西的特征.利用小震分布和区域应力场拟合得到发震断层参数为走向207°/倾角50°/滑动角92°,绝大多数余震发生在断层面附近10km左右的区域.综合地震序列分布特征、主震震源深度和已有破裂过程研究结果,可以推测主震破裂过程自初始点沿断层的两侧扩展破裂,南侧破裂比北侧稍长,滑动量主要集中在初始破裂点附近,可能没有破裂到地表.综合本文研究成果、地震烈度分布和现有的科学考察结果,初步推测发震构造为龙门山山前断裂,也不排除主震震中东侧还存在一条未知的基底断裂发震的可能性.
Based on the digital waveforms of China National Seismic Network and Sichuan Seismic Network,The Lushan earthquake sequence(ML≥2.0) was relocated precisely by HypoDD,36 best double-couple focal mechanisms(ML≥4.0) were determined by CAP method.The geometric fault parameters and slip direction were estimated by using distribution of the Lushan earthquake sequence and regional stress field.We analyzed the characteristics of focal depth,focal mechanisms and source rupture to determine the seismogenic structure.The main shock was relocated at 30.30°N,102.97°E;the depth of the initial rupture and centriod is about 15 km and 14 km,respectively;the nodal plane parameters of the best double-couple focal mechanism: strike 209°,dip 46° and slip 94°;strike 23°,dip 44° and slip 86°,respectively.The focal mechanism of main shock is pure thrust type,and most of the focal mechanisms of the aftershocks show the same rupture property as the main shock.The aftershocks(ML≥2.0) distributed in two sides of the main shock,the length of sequence is about 30 km,the focal depth is centrally distributed in 5~27 km;the focal depth of the aftershocks(ML≥3.5) is centrally distributed in 9~25 km and show the focal fault dip toward northwest.We determined the focal fault parameter: strike 207°,dip 50° and slip 92° using distribution of sequences and regional stress field,most aftershocks distributed in the 10 km vicinity of the focal plane.Combine the distribution of earthquake sequence,the focal depth of the main shock with the result of rupture process,we infer that the main rupture extend along the two sides of the fault from the initial rupture point,the southern rupture is a little longer than the northern part,the slip focus on the vicinity of the initial rupture point and the rupture is not up to the surface.Based on the results of this paper,the distribution of seismic intensity and field investigation,we speculate preliminarily the focal fault is the front fault of Longmenshan,but we do not rule out the possibility that there is an unknown base fault nearby the east of main-shock.
Based on the digital waveforms of China National Seismic Network and Sichuan Seismic Network,The Lushan earthquake sequence(ML≥2.0) was relocated precisely by HypoDD,36 best double-couple focal mechanisms(ML≥4.0) were determined by CAP method.The geometric fault parameters and slip direction were estimated by using distribution of the Lushan earthquake sequence and regional stress field.We analyzed the characteristics of focal depth,focal mechanisms and source rupture to determine the seismogenic structure.The main shock was relocated at 30.30°N,102.97°E;the depth of the initial rupture and centriod is about 15 km and 14 km,respectively;the nodal plane parameters of the best double-couple focal mechanism: strike 209°,dip 46° and slip 94°;strike 23°,dip 44° and slip 86°,respectively.The focal mechanism of main shock is pure thrust type,and most of the focal mechanisms of the aftershocks show the same rupture property as the main shock.The aftershocks(ML≥2.0) distributed in two sides of the main shock,the length of sequence is about 30 km,the focal depth is centrally distributed in 5~27 km;the focal depth of the aftershocks(ML≥3.5) is centrally distributed in 9~25 km and show the focal fault dip toward northwest.We determined the focal fault parameter: strike 207°,dip 50° and slip 92° using distribution of sequences and regional stress field,most aftershocks distributed in the 10 km vicinity of the focal plane.Combine the distribution of earthquake sequence,the focal depth of the main shock with the result of rupture process,we infer that the main rupture extend along the two sides of the fault from the initial rupture point,the southern rupture is a little longer than the northern part,the slip focus on the vicinity of the initial rupture point and the rupture is not up to the surface.Based on the results of this paper,the distribution of seismic intensity and field investigation,we speculate preliminarily the focal fault is the front fault of Longmenshan,but we do not rule out the possibility that there is an unknown base fault nearby the east of main-shock.
引文
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[8]郑勇,葛粲,谢祖军等.芦山与汶川地震震区地壳上地幔结构及深部孕震环境.中国科学:地球科学,2013,43:1027-1037.Zheng Y,Ge C,Xie Z J,et al.Crustal and upper mantlestructure and the deep seismogenic environment in the sourceregions of the Lushan earthquake and the Wenchuanearthquake.Scientia Sinica Terrae(in Chinese),2013,43:1027-1037.
[9]Waldhauser F,Ellsworth W L.A double-difference earthquakelocation algorithm:Method and application to the NorthernHayward fault.Bull.Seismol.Soc.Amer.,2000,90(6):1353-1368.
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[11]王椿镛,吴建平,楼海等.川西藏东地区的地壳P波速度结构.中国科学(D辑),2003,33(增刊):181-189.Wang C Y,Wu J P,Lou H,et al.P wave crustal velocitystructure in western Sichuan and eastern Tibetan region.Science in China(Ser.D)(in Chinese),2003,33(Suppl.):181-189.
[12]朱介寿,曹家敏,刘舜化等.用人工地震初探川西地区的地壳结构.成都地质学院学报,1984,3:111-122.Zhu J S,Cao J M,Liu S H,et al.A preliminaryinvestigation on crustal structure of western Sichuan byexplosion seismology.Bull of Chengdu Geology Institute(inChinese),1984,3:111-122.
[13]赵珠,范军,郑斯华等.龙门山推覆构造带地壳速度结构和震源位置的精确修定.地震学报,1997,19(6):615-622.Zhao Z,Fan J,Zheng S H,et al.Precision determination ofthe crustal structure and hypocentral locations in theLongmenshan thrust nappe belt.Acta Seismologica Sinica(in Chinese),1997,19(6):615-622.
[14]Zhao L S,Helmberger D V.Source estimation from broadbandregional seismograms.Bull.Seismol.Soc.Amer.,1994,84(1):91-104.
[15]Zhu L P,Helmberger D V.Advancement in source estimationtechniques using broadband regional seismograms.Bull.Seismol.Soc.Amer.,1996,86(5):1634-1641.
[16]Tan Y,Zhu L P,Helmberger D V,et al.Locating andmodeling regional earthquakes with two stations.J.Geophys.Res.,2006,111,B01306,doi:1029/2005JB003775.
[17]韦生吉,倪四道,崇加军等.2003年8月16日赤峰地震:一个可能发生在下地壳的地震.地球物理学报,2009,52(1):111-119.Wei S J,Ni S D,Chong J J,et al.The 16August 2003Chifengearthquake:Is it a lower crust earthquake.Chinese Journal ofGeophysics(in Chinese),2009,52(1):111-119.
[18]郑勇,马宏生,吕坚等.汶川地震强余震(Ms≥5.6)的震源机制解及其与发震构造的关系.中国科学(D辑),2009,39(4):413-426.Zheng Y,Ma H S,LüJ,et al.Source mechanism of strongaftershock of(Ms≥5.6)of Wenchuan earthquake and theimplication for seismotectonic.Science in China(Ser.D)(inChinese),2009,39(4):413-426.
[19]谢祖军,郑勇,倪四道等.2011年1月19日安庆ML4.8地震的震源机制解和深度研究.地球物理学报,2012,55(5):1624-1634.Xie Z J,Zheng Y,Ni S D,et al.Focal mechanism and focaldepth of the 19January 2011 Anqing earthquake.ChineseJournal of Geophysics(in Chinese),2012,55(5):1624-1634.
[20]吕坚,郑勇,倪四道等.2005年11月26日九江—瑞昌Ms5.7、Ms4.8地震的震源机制解与发震构造研究.地球物理学报,2008,51(1):158-164.LüJ,Zheng Y,Ni S D,et al.Focal mechanisms andseismogenic structures of the Ms5.7 and Ms4.8 Jiujiang-Ruichang earthquake of Nov.26,2005.Chinese Journal ofGeophysics(in Chinese),2008,51(1):158-164.
[21]吕坚,苏金蓉,靳玉科等.汶川8.0级地震序列重新定位及其发震构造初探.地震地质,2008,30(4):917-925.LüJ,Su J R,Jin Y K,et al.Discussion on relocation andseismo-tectonics of the MS8.0 Wenchuan earthquake sequences.Seismology and Geology(in Chinese),2008,30(4):917-925.
[22]Zheng Y,Ni S D,Xie Z J,et al.Strong aftershocks in thenorthern segment of the Wenchuan earthquake rupture zoneand their seismotectonic implications.Earth Planets Space,2010,62:881-886.
[23]郑秀芬,欧阳飚,张东宁等.“国家数字测震台网数据备份中心”技术系统建设及其对汶川大地震研究的数据支撑.地球物理学报,2009,52(5):1412-1417.Zheng X F,Ouyang B,Zhang D N,et al.Technical systemconstruction of Data Backup Centre for China SeismographNetwork and the data support to researches on the Wenchuanearthquake.Chinese Journal of Geophysics(in Chinese),2009,52(5):1412-1417.
[24]万永革,沈正康,刁桂苓等.利用小震分布和区域应力场确定大震断层面参数方法及其在唐山地震序列中的应用.地球物理学报,2008,51(3):793-804.Wan Y G,Shen Z K,Diao G L,et al.An algorithm of faultparameter determination using distribution of small earthquakesand parameter of regional stress field and its application toTangshan earthquake sequence.Chinese Journal of Geophysics(in Chinese),2008,51(3):793-804.
[25]徐锡伟,陈桂华,于贵华等.5.12汶川地震地表破裂基本参数的再论证及其构造内涵分析.地球物理学报,2010,53(10):2321-2336.Xu X W,Chen G H,Yu G H,et al.Reevaluation of surfacerupture parameters of the 5.12Wenchuan earthquake and itstectonic implication for Tibetan uplift.Chinese Journal ofGeophysics(in Chinese),2010,53(10):2321-2336.
[2]曾祥方,罗艳,韩立波等.2013年4月20日四川芦山Ms7.0地震:一个高角度逆冲地震.地球物理学报,2013,56(4):1418-1424.Zeng X F,Luo Y,Han L B,et al.The Lushan Ms7.0earthquake on 20 April 2013:A high-angle thrust event.Chinese Journal of Geophysics(in Chinese),2013,56(4):1418-1424.
[3]张勇,许力生,陈运泰.芦山4.20地震破裂过程及其致灾特征初步分析.地球物理学报,2013,56(4):1408-1411.Zhang Y,Xu L S,Chen Y T.Rupture process of the Lushan4.20earthquake and preliminary analysis on the disaster-causing mechanism.Chinese Journal of Geophysics(in Chinese),2013,56(4):1408-1411.
[4]王卫民,郝金来,姚振兴.2013年4月20日四川芦山地震震源破裂过程反演初步结果.地球物理学报,2013,56(4):1412-1417.Wang W M,Hao J L,Yao Z X.Preliminary result forrupture process of Apr.20,2013,Lushan Earthquake,Sichuan,China.Chinese Journal of Geophysics(in Chinese),2013,56(4):1412-1417.
[5]刘成利,郑勇,葛粲等.2013年芦山7.0级地震的动态破裂过程.中国科学:地球科学,2013,43:1020-1026.Liu C L,Zheng Y,Ge C,et al.Rupture process of the M7.0Lushan Earthquake,2013.Scientia Sinica Terrae(inChinese),2013,43:1020-1026.
[6]谢祖军,金笔凯,郑勇等.近远震波形反演2013年芦山地震震源参数.中国科学:地球科学,2013,43:1010-1019.Xie Z J,Jin B K,Zheng Y,et al.Source parametersinversion of the 2013 Lushan earthquake by combiningteleseismic waveforms and local seismograms.Scientia SinicaTerrae(in Chinese),2013,43:1010-1019.
[7]单斌,熊熊,郑勇等.2013年芦山地震导致的周边断层应力变化及其与2008年汶川地震的关系.中国科学:地球科学,2013,43:1002-1009.Shan B,Xiong X,Zheng Y,et al.Stress changes on majorfaults caused by 2013Lushan earthquake,and its relationshipwith 2008Wenchuan earthquake.Scientia Sinica Terrae(inChinese),2013,43:1002-1009.
[8]郑勇,葛粲,谢祖军等.芦山与汶川地震震区地壳上地幔结构及深部孕震环境.中国科学:地球科学,2013,43:1027-1037.Zheng Y,Ge C,Xie Z J,et al.Crustal and upper mantlestructure and the deep seismogenic environment in the sourceregions of the Lushan earthquake and the Wenchuanearthquake.Scientia Sinica Terrae(in Chinese),2013,43:1027-1037.
[9]Waldhauser F,Ellsworth W L.A double-difference earthquakelocation algorithm:Method and application to the NorthernHayward fault.Bull.Seismol.Soc.Amer.,2000,90(6):1353-1368.
[10]王椿镛,韩渭宾,吴建平等.松潘—甘孜造山带地壳速度结构.地震学报,2003,25(3):229-241.Wang C Y,Han W B,Wu J P,et al.Crustal structurebeneath the Songpan-Ganzi orogenic belt.Acta SeismologicaSinica(in Chinese),2003,25(3):229-241.
[11]王椿镛,吴建平,楼海等.川西藏东地区的地壳P波速度结构.中国科学(D辑),2003,33(增刊):181-189.Wang C Y,Wu J P,Lou H,et al.P wave crustal velocitystructure in western Sichuan and eastern Tibetan region.Science in China(Ser.D)(in Chinese),2003,33(Suppl.):181-189.
[12]朱介寿,曹家敏,刘舜化等.用人工地震初探川西地区的地壳结构.成都地质学院学报,1984,3:111-122.Zhu J S,Cao J M,Liu S H,et al.A preliminaryinvestigation on crustal structure of western Sichuan byexplosion seismology.Bull of Chengdu Geology Institute(inChinese),1984,3:111-122.
[13]赵珠,范军,郑斯华等.龙门山推覆构造带地壳速度结构和震源位置的精确修定.地震学报,1997,19(6):615-622.Zhao Z,Fan J,Zheng S H,et al.Precision determination ofthe crustal structure and hypocentral locations in theLongmenshan thrust nappe belt.Acta Seismologica Sinica(in Chinese),1997,19(6):615-622.
[14]Zhao L S,Helmberger D V.Source estimation from broadbandregional seismograms.Bull.Seismol.Soc.Amer.,1994,84(1):91-104.
[15]Zhu L P,Helmberger D V.Advancement in source estimationtechniques using broadband regional seismograms.Bull.Seismol.Soc.Amer.,1996,86(5):1634-1641.
[16]Tan Y,Zhu L P,Helmberger D V,et al.Locating andmodeling regional earthquakes with two stations.J.Geophys.Res.,2006,111,B01306,doi:1029/2005JB003775.
[17]韦生吉,倪四道,崇加军等.2003年8月16日赤峰地震:一个可能发生在下地壳的地震.地球物理学报,2009,52(1):111-119.Wei S J,Ni S D,Chong J J,et al.The 16August 2003Chifengearthquake:Is it a lower crust earthquake.Chinese Journal ofGeophysics(in Chinese),2009,52(1):111-119.
[18]郑勇,马宏生,吕坚等.汶川地震强余震(Ms≥5.6)的震源机制解及其与发震构造的关系.中国科学(D辑),2009,39(4):413-426.Zheng Y,Ma H S,LüJ,et al.Source mechanism of strongaftershock of(Ms≥5.6)of Wenchuan earthquake and theimplication for seismotectonic.Science in China(Ser.D)(inChinese),2009,39(4):413-426.
[19]谢祖军,郑勇,倪四道等.2011年1月19日安庆ML4.8地震的震源机制解和深度研究.地球物理学报,2012,55(5):1624-1634.Xie Z J,Zheng Y,Ni S D,et al.Focal mechanism and focaldepth of the 19January 2011 Anqing earthquake.ChineseJournal of Geophysics(in Chinese),2012,55(5):1624-1634.
[20]吕坚,郑勇,倪四道等.2005年11月26日九江—瑞昌Ms5.7、Ms4.8地震的震源机制解与发震构造研究.地球物理学报,2008,51(1):158-164.LüJ,Zheng Y,Ni S D,et al.Focal mechanisms andseismogenic structures of the Ms5.7 and Ms4.8 Jiujiang-Ruichang earthquake of Nov.26,2005.Chinese Journal ofGeophysics(in Chinese),2008,51(1):158-164.
[21]吕坚,苏金蓉,靳玉科等.汶川8.0级地震序列重新定位及其发震构造初探.地震地质,2008,30(4):917-925.LüJ,Su J R,Jin Y K,et al.Discussion on relocation andseismo-tectonics of the MS8.0 Wenchuan earthquake sequences.Seismology and Geology(in Chinese),2008,30(4):917-925.
[22]Zheng Y,Ni S D,Xie Z J,et al.Strong aftershocks in thenorthern segment of the Wenchuan earthquake rupture zoneand their seismotectonic implications.Earth Planets Space,2010,62:881-886.
[23]郑秀芬,欧阳飚,张东宁等.“国家数字测震台网数据备份中心”技术系统建设及其对汶川大地震研究的数据支撑.地球物理学报,2009,52(5):1412-1417.Zheng X F,Ouyang B,Zhang D N,et al.Technical systemconstruction of Data Backup Centre for China SeismographNetwork and the data support to researches on the Wenchuanearthquake.Chinese Journal of Geophysics(in Chinese),2009,52(5):1412-1417.
[24]万永革,沈正康,刁桂苓等.利用小震分布和区域应力场确定大震断层面参数方法及其在唐山地震序列中的应用.地球物理学报,2008,51(3):793-804.Wan Y G,Shen Z K,Diao G L,et al.An algorithm of faultparameter determination using distribution of small earthquakesand parameter of regional stress field and its application toTangshan earthquake sequence.Chinese Journal of Geophysics(in Chinese),2008,51(3):793-804.
[25]徐锡伟,陈桂华,于贵华等.5.12汶川地震地表破裂基本参数的再论证及其构造内涵分析.地球物理学报,2010,53(10):2321-2336.Xu X W,Chen G H,Yu G H,et al.Reevaluation of surfacerupture parameters of the 5.12Wenchuan earthquake and itstectonic implication for Tibetan uplift.Chinese Journal ofGeophysics(in Chinese),2010,53(10):2321-2336.
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