汶川M_s 8.0级地震断层间相互作用及其对起始破裂段的启示
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摘要
汶川地震在地表形成了北东向与北西向两个方向的地表破裂带,余震分布也清晰地显示沿着小鱼洞断裂存在一条北西向小震密集条带。为了研究北西向小鱼洞断裂在汶川地震破裂过程中的作用,在已有的地表破裂数据和认识的基础上,结合汶川地震前小震资料和余震资料,完善了汶川地震震源构造模型。分别计算了以北川—映秀断裂西南的虹口段(BY1)与小鱼洞断裂作为初始破裂段所产生的库仑静应力变化量(ΔCFS)分布图像。结果显示,以北川—映秀断裂虹口段(BY1)做为起始破裂段,虽然小鱼洞断裂西北段(XYD2)的局部地段处于应力触发区,但在出现地表破裂的小鱼洞断裂东南段(XYD1)却处于1.5 bar的应力抑制区,同时随着北川—映秀断裂向北东方向的进一步破裂,小鱼洞断裂仍处于应力抑制区,并且范围有所扩大。如果这样,在汶川地震过程中,小鱼洞断裂应该是稳定的,不可能产生地表破裂带及小震密集条带;以小鱼洞断裂作为起始破裂段,北川—映秀断裂BY1段的大部分区段处于1.0～1.5 bar的应力触发区,不但如此,小鱼洞断裂对彭灌断裂也有触发作用。基于以上结果,认为汶川地震破裂过程是以北西向小鱼洞断裂为起始破裂段,该断裂的破裂触发了北川—映秀断裂和彭灌断裂,并导致北川—映秀断裂向北东方向发生级联破裂。
The 2008 Wenchuan Ms 8.0 earthquake has produced two long NE trending rupture zones as well as a short NW-strike rupture zone on the surface.The latter one is consistent with the Xiaoyudong fault and the distribution of aftershocks,and has been paid less attention.We speculate that this NW-directed fault may play a certain role during the main shock process.To test this idea,we established a seismic source model comprising three faults,the NE trending Beichuan-Yingxiu fault,the Pengguan fault,and the NW trending Xiaoyudong fault,and calculated Coulomb failure stress change during the source rupture.We considered two cases for the model.One is that the southwestern section of the NE directed Beichuan-Yingxiu fault served as the initial rupture.And the other is that the NW trending Xiaoyudong fault ruptured first during the main shock process.Under the first condition,most of the Xiaoyudong fault was inhibited by 1.5 bar Coulomb stress from failure(the stress shadows),though its northwestern section was in the stress trigger region.With the rupture of the Beichuan-Yingxiu fault spreaded toward NE,the stress shadowed on the Xiaoyudong fault became larger.If such a process was true,then the Xiaoyudong fault should had been stable during the main shock of the Wenchuan Ms 8.0 event and no surface ruptures and small aftershocks would have occurred along this NW trending fault.Evidently this is in contrary to the fact.Under the second condition,the Xiaoyudong fault ruptured first,and then other faults failed successively.In response to the initial rupture on the Xiaoyudong fault,most of the southwestern section of the Beichuan-Yingxiu fault was in the stress trigger region of 1.01.5 bar,and the parallel Pengguan fault was also brought closer to failure,implying the whole source fault system started to rupture toward northeast,in agreement with the observations.Thus,this study suggests that the NW trending Xiaoyudong fault should have been the initial rupturing member that triggered the NE directed Beichuan-Yingxiu fault and Pengguan fault to fail leading to the main shock.
The 2008 Wenchuan Ms 8.0 earthquake has produced two long NE trending rupture zones as well as a short NW-strike rupture zone on the surface.The latter one is consistent with the Xiaoyudong fault and the distribution of aftershocks,and has been paid less attention.We speculate that this NW-directed fault may play a certain role during the main shock process.To test this idea,we established a seismic source model comprising three faults,the NE trending Beichuan-Yingxiu fault,the Pengguan fault,and the NW trending Xiaoyudong fault,and calculated Coulomb failure stress change during the source rupture.We considered two cases for the model.One is that the southwestern section of the NE directed Beichuan-Yingxiu fault served as the initial rupture.And the other is that the NW trending Xiaoyudong fault ruptured first during the main shock process.Under the first condition,most of the Xiaoyudong fault was inhibited by 1.5 bar Coulomb stress from failure(the stress shadows),though its northwestern section was in the stress trigger region.With the rupture of the Beichuan-Yingxiu fault spreaded toward NE,the stress shadowed on the Xiaoyudong fault became larger.If such a process was true,then the Xiaoyudong fault should had been stable during the main shock of the Wenchuan Ms 8.0 event and no surface ruptures and small aftershocks would have occurred along this NW trending fault.Evidently this is in contrary to the fact.Under the second condition,the Xiaoyudong fault ruptured first,and then other faults failed successively.In response to the initial rupture on the Xiaoyudong fault,most of the southwestern section of the Beichuan-Yingxiu fault was in the stress trigger region of 1.01.5 bar,and the parallel Pengguan fault was also brought closer to failure,implying the whole source fault system started to rupture toward northeast,in agreement with the observations.Thus,this study suggests that the NW trending Xiaoyudong fault should have been the initial rupturing member that triggered the NE directed Beichuan-Yingxiu fault and Pengguan fault to fail leading to the main shock.
引文
[1]Chen Y T,Xu L S,Zhang Y,et al.Report of the GreatWenchuan Earthquake Source of May 12,2008[R].SeismicInformation Network of China,2008[2008-05-18]http:∥www.csi.ac.cn/sichuan/chenyuntai.pdf(in Chinese).
[2]Liu C,Zhang Y,Xu L S,et al.Anewtechnique for momenttensor inversion with applications to the 2008 WenchuanMs8.0 earthquake sequence[J].Acta Seismologica Sinica,2008,30(4):329-339(in Chinese).
[3]Wang W M,Zhao L F,Li J,et al.Rupture process of the 8.0Wenchuan earthquake of Sichuan,China[J].Chinese Journal ofGeophysics,2008,51(5):1403-1410(in Chinese).
[4]Shen Z K,Sun J B,Zhang P Z,et al.Slip maxi ma at faultand rupturing of barriers during the 2008 Wenchuan earth-quake[J].Nature Geoscience,2009(2):718-724.
[5]Xu X W,Wen X Z,Ye J Q,et al.TheMs8.0 Wenchuanearthquake surface rupture and its seismogenic structure[J].Seismology and Geology,2008,30(3):597-629(in Chinese).
[6]Xu X W,Wen X Z,Yu G H,et al.Coseismic reverse-andoblique-slip surface faulting generated by the 2008Mw7.9Wenchuan earthquake[J].Geological Society of America,2009,37(6):515-518.
[7]Chen G H,Xu X W,Yu G H,et al.Co-seismic slip and slippartitioning of multi-faults during theMs8.0 2008 Wenchuanearthquake[J].Chinese Journal of Geophysics,2009,52(5):1385-1391(in Chinese).
[8]Zhang S C,Diao G L,Wang S J,et al.Rupture characteris-tics of the 1976 Longling earthquake sequence[J].EarthquakeResearchin China,1994,10(2):152-159(in Chinese).
[9]Zheng Y,Ma HS,LüJ,et al.The relationship betweenthefocal mechanismin strong aftershock and seismogenic struc-ture in Wenchuan earthquake[J].Sciencein China:Series D,2009,39(4):413-426(in Chinese).
[10]Chen S F,Deng Q D,Zhao X L,et al.Evolutionary historyand deformation mechanism of central Longmenshan thrust-nappes and related tectonics[J].Seismology and Geology,1994,16(4):389-403(in Chinese).
[11]Deng Q D,Chen S F,Zhao X L.Tectonics,seismisity anddynamics of Longmenshan mountains andits adjacent regions[J].Seismology and Geology,1994,16(4):389-403(in Chi-nese).
[12]Ran Y K,Chen L C,Chen G H,et al.Pri mary analysis ofin-situ recurrence of large earthquake along seismogenic faultof theMs8.0 Wenchuan earthquake[J].Seismology and Ge-ology,2008,30(3):630-643(in Chinese).
[13]Han Z J,Dong S P,Xie F R,et al.Earthquake triggering bystatic stress:The 5 major earthquakes withM≥7(15611920)in the northern section of south-north seismic zone,China[J].Chinese Journal of Geophysics,2008,51(6):1776-1784(in Chinese).
[14]Harris R.Introduction to special section:Stress triggers,stress shadows,andi mplications for seismic hazard[J].Jour-nal of Geophysical Research,1998,103(24):347-358.
[15]Parson T,Ji C.Stress change from the 2008 Wenchuanearthquake andincreased hazardinthe Sichuan Basin[J].Na-ture,2008,454:509-510.
[16]Wan Y G,Shen Z K,Sheng S Z,et al.Theinfluence of 2008Wenchuan earthquake on surrounding faults[J].Acta Seis-mologica Sinica,2009,31(2):128-139(in Chinese).
[17]Wan Y G,Wu Z L,Zhou G W,et al.Research on seismicstress triggering[J].Acta Seismologica Sinica,2002,24(5):533-551(in Chinese).
[18]Toda S,Lin J,Meghraoui M,et al.12 May 2008M=7.9Wenchuan,China,earthquake calculated to increase failurestress and seismicity rate on three major fault systems[J].Geophysical Research Letters,2008,35,doi:10.1029/2008GL034903.
[19]Toda S,Stein RS,Dinger K R,et al.Forecastingthe evolu-tion of seismicity in southern California:Ani mation built onearthquake stress transfer[J].Journal of Geophysical Re-search,2005,110(B05),doi:10.1029/2004JB003415.
[20]Okada Y.Internal deformation due to shear and tensile faultsin a half space[J].Bulletin of the Seismological Society of A-merica,1992,82(2):1018-1040.
[21]King G,Cocco M.Fault interaction by elastic stress chan-ges:New clues from earthquake sequence[J].Advances inGeophysics,2001,44:1-38.
[22]Lin J,Stein R S.Stress triggering in thrust and subductionearthquake,and stress interaction between the southern SanAndreas and nearby thrust and strike-slip faults[J].Journalof Geophysical Research,2004,109,B02303,doi:10.1029/2003JB002607.
[23]Zhu H,Wen X Z.Stress triggering process of the 1973 to1976 Songpan,Sichuan,sequence of strong earthquakes[J].Chinese Journal of Geophysics,2009,52(4):994-1003(inChinese).
[24]Chen J H,Liu Q Y,Li S C,et al.Seismotectonic study byrelocation of the WenchuanMs8.0 earthquake sequence[J].Chinese Journal of Geophysics,2009,52(2):390-397(inChinese).
[25]Zhang S C.Studies of conjugate seismotectonics of the conti-nental earthquake in China[J].Earthquake Research in Chi-na,1991,7(2):69-76(in Chinese).
[26]Cheng WZ.Several hot pots in earthquake forecast[J].Sci-ence and Technology Innovation Herald,2009,16:237-238(in Chinese).
[1]陈云泰,许力生,张勇,等.2008年5月12日汶川特大地震震源特性分析报告[R].中国地震信息网,2008[2008-05-18]http:∥www.csi.ac.cn/sichuan/chenyuntai.pdf.
[2]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.
[3]王卫民,赵连峰,李娟,等.四川汶川8.0级地震震源过程[J].地球物理学报,2008,51(5):1403-1410.
[5]徐锡伟,闻学泽,叶建青,等.汶川Ms8.0地震地表破裂带及其发震构造[J].地震地质,2008,30(3):597-629.
[7]陈桂华,徐锡伟,于贵华,等.2008年汶川Ms8.0地震多断裂破裂的近地表同震位移滑移及滑移分解[J].地球物理学报,2009,52(5):1385-1391.
[8]张四昌,刁桂苓,王绍晋,等.1976年龙陵震群序列的破裂特征[J].中国地震,1994,10(2):152-159.
[9]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[J].中国科学:D辑,2009,39(4):413-426.
[10]陈社发,邓起东,赵小麟,等.龙门山中段推覆构造带及相关构造的演化历史和变形机制[J].地震地质,1994,16(4):389-403.
[11]邓起东,陈社发,赵小麟.龙门山及其邻区的构造和地震活动及动力学[J].地震地质,1994,16(4):389-403.
[12]冉勇康,陈立春,陈桂华,等.汶川Ms8.0地震发震断裂大地震原地重复现象初析[J].地震地质,2008,30(3):630-643.
[13]韩竹军,董绍鹏,谢富任,等.南北地震带北部5次(1561—1920年)M≥7级地震触发关系研究[J].地球物理学报,2008,51(6):1776-1784.
[16]万永革,沈正康,盛书中,等.2008年汶川大地震对周围断层的影响[J].地震学报,2009,31(2):128-139.
[17]万永革,吴忠良,周公威,等.地震应力触发研究[J].地震学报,2002,24(5):533-551.
[23]朱航,闻学泽.1973—1976年四川松潘强震序列的应力触发过程[J].地球物理学报,2009,52(4):994-1003.
[24]陈九辉,刘启元,李顺成,等.汶川Ms8.0地震余震序列重新定位及其地震构造研究[J].地球物理学报,2009,52(2):390-397.
[25]张四昌.中国大陆共轭地震构造研究[J].中国地震,1991,7(2):69-76.
[26]程万正.论地震预报的几个热点问题[J].科技创新导报,2009,16:237-238.
[2]Liu C,Zhang Y,Xu L S,et al.Anewtechnique for momenttensor inversion with applications to the 2008 WenchuanMs8.0 earthquake sequence[J].Acta Seismologica Sinica,2008,30(4):329-339(in Chinese).
[3]Wang W M,Zhao L F,Li J,et al.Rupture process of the 8.0Wenchuan earthquake of Sichuan,China[J].Chinese Journal ofGeophysics,2008,51(5):1403-1410(in Chinese).
[4]Shen Z K,Sun J B,Zhang P Z,et al.Slip maxi ma at faultand rupturing of barriers during the 2008 Wenchuan earth-quake[J].Nature Geoscience,2009(2):718-724.
[5]Xu X W,Wen X Z,Ye J Q,et al.TheMs8.0 Wenchuanearthquake surface rupture and its seismogenic structure[J].Seismology and Geology,2008,30(3):597-629(in Chinese).
[6]Xu X W,Wen X Z,Yu G H,et al.Coseismic reverse-andoblique-slip surface faulting generated by the 2008Mw7.9Wenchuan earthquake[J].Geological Society of America,2009,37(6):515-518.
[7]Chen G H,Xu X W,Yu G H,et al.Co-seismic slip and slippartitioning of multi-faults during theMs8.0 2008 Wenchuanearthquake[J].Chinese Journal of Geophysics,2009,52(5):1385-1391(in Chinese).
[8]Zhang S C,Diao G L,Wang S J,et al.Rupture characteris-tics of the 1976 Longling earthquake sequence[J].EarthquakeResearchin China,1994,10(2):152-159(in Chinese).
[9]Zheng Y,Ma HS,LüJ,et al.The relationship betweenthefocal mechanismin strong aftershock and seismogenic struc-ture in Wenchuan earthquake[J].Sciencein China:Series D,2009,39(4):413-426(in Chinese).
[10]Chen S F,Deng Q D,Zhao X L,et al.Evolutionary historyand deformation mechanism of central Longmenshan thrust-nappes and related tectonics[J].Seismology and Geology,1994,16(4):389-403(in Chinese).
[11]Deng Q D,Chen S F,Zhao X L.Tectonics,seismisity anddynamics of Longmenshan mountains andits adjacent regions[J].Seismology and Geology,1994,16(4):389-403(in Chi-nese).
[12]Ran Y K,Chen L C,Chen G H,et al.Pri mary analysis ofin-situ recurrence of large earthquake along seismogenic faultof theMs8.0 Wenchuan earthquake[J].Seismology and Ge-ology,2008,30(3):630-643(in Chinese).
[13]Han Z J,Dong S P,Xie F R,et al.Earthquake triggering bystatic stress:The 5 major earthquakes withM≥7(15611920)in the northern section of south-north seismic zone,China[J].Chinese Journal of Geophysics,2008,51(6):1776-1784(in Chinese).
[14]Harris R.Introduction to special section:Stress triggers,stress shadows,andi mplications for seismic hazard[J].Jour-nal of Geophysical Research,1998,103(24):347-358.
[15]Parson T,Ji C.Stress change from the 2008 Wenchuanearthquake andincreased hazardinthe Sichuan Basin[J].Na-ture,2008,454:509-510.
[16]Wan Y G,Shen Z K,Sheng S Z,et al.Theinfluence of 2008Wenchuan earthquake on surrounding faults[J].Acta Seis-mologica Sinica,2009,31(2):128-139(in Chinese).
[17]Wan Y G,Wu Z L,Zhou G W,et al.Research on seismicstress triggering[J].Acta Seismologica Sinica,2002,24(5):533-551(in Chinese).
[18]Toda S,Lin J,Meghraoui M,et al.12 May 2008M=7.9Wenchuan,China,earthquake calculated to increase failurestress and seismicity rate on three major fault systems[J].Geophysical Research Letters,2008,35,doi:10.1029/2008GL034903.
[19]Toda S,Stein RS,Dinger K R,et al.Forecastingthe evolu-tion of seismicity in southern California:Ani mation built onearthquake stress transfer[J].Journal of Geophysical Re-search,2005,110(B05),doi:10.1029/2004JB003415.
[20]Okada Y.Internal deformation due to shear and tensile faultsin a half space[J].Bulletin of the Seismological Society of A-merica,1992,82(2):1018-1040.
[21]King G,Cocco M.Fault interaction by elastic stress chan-ges:New clues from earthquake sequence[J].Advances inGeophysics,2001,44:1-38.
[22]Lin J,Stein R S.Stress triggering in thrust and subductionearthquake,and stress interaction between the southern SanAndreas and nearby thrust and strike-slip faults[J].Journalof Geophysical Research,2004,109,B02303,doi:10.1029/2003JB002607.
[23]Zhu H,Wen X Z.Stress triggering process of the 1973 to1976 Songpan,Sichuan,sequence of strong earthquakes[J].Chinese Journal of Geophysics,2009,52(4):994-1003(inChinese).
[24]Chen J H,Liu Q Y,Li S C,et al.Seismotectonic study byrelocation of the WenchuanMs8.0 earthquake sequence[J].Chinese Journal of Geophysics,2009,52(2):390-397(inChinese).
[25]Zhang S C.Studies of conjugate seismotectonics of the conti-nental earthquake in China[J].Earthquake Research in Chi-na,1991,7(2):69-76(in Chinese).
[26]Cheng WZ.Several hot pots in earthquake forecast[J].Sci-ence and Technology Innovation Herald,2009,16:237-238(in Chinese).
[1]陈云泰,许力生,张勇,等.2008年5月12日汶川特大地震震源特性分析报告[R].中国地震信息网,2008[2008-05-18]http:∥www.csi.ac.cn/sichuan/chenyuntai.pdf.
[2]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.
[3]王卫民,赵连峰,李娟,等.四川汶川8.0级地震震源过程[J].地球物理学报,2008,51(5):1403-1410.
[5]徐锡伟,闻学泽,叶建青,等.汶川Ms8.0地震地表破裂带及其发震构造[J].地震地质,2008,30(3):597-629.
[7]陈桂华,徐锡伟,于贵华,等.2008年汶川Ms8.0地震多断裂破裂的近地表同震位移滑移及滑移分解[J].地球物理学报,2009,52(5):1385-1391.
[8]张四昌,刁桂苓,王绍晋,等.1976年龙陵震群序列的破裂特征[J].中国地震,1994,10(2):152-159.
[9]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[J].中国科学:D辑,2009,39(4):413-426.
[10]陈社发,邓起东,赵小麟,等.龙门山中段推覆构造带及相关构造的演化历史和变形机制[J].地震地质,1994,16(4):389-403.
[11]邓起东,陈社发,赵小麟.龙门山及其邻区的构造和地震活动及动力学[J].地震地质,1994,16(4):389-403.
[12]冉勇康,陈立春,陈桂华,等.汶川Ms8.0地震发震断裂大地震原地重复现象初析[J].地震地质,2008,30(3):630-643.
[13]韩竹军,董绍鹏,谢富任,等.南北地震带北部5次(1561—1920年)M≥7级地震触发关系研究[J].地球物理学报,2008,51(6):1776-1784.
[16]万永革,沈正康,盛书中,等.2008年汶川大地震对周围断层的影响[J].地震学报,2009,31(2):128-139.
[17]万永革,吴忠良,周公威,等.地震应力触发研究[J].地震学报,2002,24(5):533-551.
[23]朱航,闻学泽.1973—1976年四川松潘强震序列的应力触发过程[J].地球物理学报,2009,52(4):994-1003.
[24]陈九辉,刘启元,李顺成,等.汶川Ms8.0地震余震序列重新定位及其地震构造研究[J].地球物理学报,2009,52(2):390-397.
[25]张四昌.中国大陆共轭地震构造研究[J].中国地震,1991,7(2):69-76.
[26]程万正.论地震预报的几个热点问题[J].科技创新导报,2009,16:237-238.
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