汶川M_s8级地震形成的擦痕形迹及其意义探讨
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摘要
2008年5月12日14时28分(北京时间)中国四川省汶川县境内发生里氏8.0级地震。北川—映秀断裂是汶川Ms8级地震的发震断裂之一,以逆(右行)走滑活动为主,延伸长约220km,活动强度大于其他两条断裂。主震在北川—映秀地表破裂带局部地点形成清晰的擦痕,它的位置和规模可能是深部破裂滑动量峰值在地表的响应。根据断层擦痕反映的应力场及位移与破裂长度关系等特征,将北川—映秀破裂带分为虹口段、北川段、南坝段。虹口段长度约22～45km,同震位移量约4.5m,σ1呈NWW—NW向,至少经历了三期活动,第三期逆冲活动强度最大,改造前两期逆(右行)走滑活动,它们的形成可能均与本次主震相关;北川段长约90～100km,同震位移量约3.5m,σ1呈NWW向近水平,活动强度弱于虹口第三期;南坝段长约35～50km,同震位移量约2.5m,以NWW向近水平挤压为特征,σ1方位角与中、南段相差约180°,活动强度与南段前两期相近。
On May 12th,2008,a great Ms 8.0 earthquake occurred in Wenchuan County,Sichuan Province.The Beichuan-Yingxiu fault extending about 220 km characterized by dextral strike-slip faulting is one of the three main seismogenic faults along the Longmenshan Fault zone,and its activity is much more important than the other two.The major shock had induced clear striations presenting at some local places along the rupture of the Beichuan-Yingxiu fault,the location and size of the striations may be the surface response to the peak value of the deep rupture.Based on the stress field reflected by the striations and on the relationship between displacement and surface rupture length,the Beichuan-Yingxiu rupture zone are able to be subdivided into three segments,namely the Hongkou subsection,the Beichuan subsection and the Nanba subsection.Among them,Hongkou subsection extends 22-45 km,with coseismic displacement of 4.5 m with σ1 stress in the direction of NWW-NW,which had undergone at least three phases of activation.It is indicated that the phase Ⅲ is the most intensive reverse faulting which reconstructs the phaseⅠandⅡ dextral strike slip activity,which all are controlled by the main shock.The Beichuan subsection extends 90-100 km,with coseismic displacement of 3.5 m,and σ1 stress in the direction of NWW and is approximately horizontal,and its intensity is weaker than the phase III of Hongkou.The Nanba subsection extends 35-50 km,with coseismic displacement of 2.5 m and σ1 stress in the direction of NWW characterized by nearly horizontal compression.The σ1 azimuth is 180°different from those of the south and middle segments,and its intensity is similar to that of the phaseⅠandⅡ of the south segment.
On May 12th,2008,a great Ms 8.0 earthquake occurred in Wenchuan County,Sichuan Province.The Beichuan-Yingxiu fault extending about 220 km characterized by dextral strike-slip faulting is one of the three main seismogenic faults along the Longmenshan Fault zone,and its activity is much more important than the other two.The major shock had induced clear striations presenting at some local places along the rupture of the Beichuan-Yingxiu fault,the location and size of the striations may be the surface response to the peak value of the deep rupture.Based on the stress field reflected by the striations and on the relationship between displacement and surface rupture length,the Beichuan-Yingxiu rupture zone are able to be subdivided into three segments,namely the Hongkou subsection,the Beichuan subsection and the Nanba subsection.Among them,Hongkou subsection extends 22-45 km,with coseismic displacement of 4.5 m with σ1 stress in the direction of NWW-NW,which had undergone at least three phases of activation.It is indicated that the phase Ⅲ is the most intensive reverse faulting which reconstructs the phaseⅠandⅡ dextral strike slip activity,which all are controlled by the main shock.The Beichuan subsection extends 90-100 km,with coseismic displacement of 3.5 m,and σ1 stress in the direction of NWW and is approximately horizontal,and its intensity is weaker than the phase III of Hongkou.The Nanba subsection extends 35-50 km,with coseismic displacement of 2.5 m and σ1 stress in the direction of NWW characterized by nearly horizontal compression.The σ1 azimuth is 180°different from those of the south and middle segments,and its intensity is similar to that of the phaseⅠandⅡ of the south segment.
引文
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[21]Doblas M,Mahecha V,Hoyos M,et al.Slickenside and fault surface kinematic indicators on active normal faults of the Alpine Betic cordilleras,Granada,Southern Spain[J].J Struct Geol,1997,19:159-170.
[22]Doblas M.Slickenside kinematicindicators[J].Tectonophys-ics,1998,295:187-197.
[23]Xu X W,Wen X Z,Ye J Q,et al.TheMs8.0Wenchuan earthquake surface ruptures andits seismogenic structure[J].Seismology and Geology,2008,30(3):597-629(in Chi-nese).
[1]中国地震台网中心.四川汶川县Ms8.0地震参数[OL/R].[2008-08-20].http:∥219.143.71.221/manage/fastReport.jsp-id=8a85532219b131b40119dba5e2c7011b.
[3]陈运泰,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[OL/R].[2008-08-20].http:∥www.csi.ac.cn/sichuan/chenyuntai.pdf.
[4]王卫民,赵连锋,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.
[7]罗立志.龙门山造山带岩石圈演化的动力学模式[J].成都地质学院学报,1991,18(1):1-7.
[8]许志琴,侯立玮,王宗秀,等.中国松潘甘孜造山带的造山过程[M].北京:地质出版社,1992:73-87.
[9]许志琴,杨经绥,姜枚,等.大陆俯冲作用及青藏高原周缘造山带的崛起[J].地学前缘,1999,6(3):139-151.
[10]邓起东,陈社发,赵小麟,等.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):389-402.
[11]李勇,周荣军,Densmore A L,等.青藏高原东缘大陆动力学过程与地质响应[M].北京:地质出版社,2006:1-134.
[13]赵小麟,邓起东,陈社发.龙门山逆断裂带中段的构造地貌学研究[J].地震地质,1994,16(4):422-428.
[14]马保起,苏刚,侯治华,等.利用岷江阶地的变形估算龙门山断裂带中段晚第四纪滑动速率[J].地震地质,2005,27(2):234-242.
[16]唐荣昌,韩渭宾.四川活动断裂与地震[M].北京:地震出版社,1993.
[17]丁国瑜,田勤俭,孔凡臣,等.活断层分段:原则、方法及应用[M].北京:地震出版社,1993.
[20]万天丰.构造应力场研究的新进展[J].地学前缘,1995,2(2):226-235.
[23]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.
[2]USGS.Magnitude7.9-Eastern Sichuan,China[OL/R].[2008-08-20].http:∥earthquake.usgs.gov/eqcenter/eqinthenews/2008/us2008ryan/.
[3]Chen Y T,Xu L S,Zhang Y,et al.Report onthe Great We-chuan Earthquake Source of May12,2008[OL/R].[2008-08-20].http:∥www.csi.ac.cn/sichuan/chenyuntai.pdf(in Chinese).
[4]Wang W M,Zhao L F,Li J,et al.Rupture process of the Ms8.0Wenchuan earthquake of Sichuan,China[J].ChineseJ Geophys,2008,51(5):1403-1410(in Chinese).
[5]Ji C,Hayes G.Preliminary result of the May12,2008Mw7.9Eastern Sichuan,China Earthquake[OL/R].[2008-08-20].http:∥earthquake.usgs.gov/eqcenter/eqinthenews/2008/us2008ryan/finite-fault.php.
[6]Parsons T,Ji C,Kirby E.Stress changes from the2008Wenchuan earthquake andincreased hazardinthe Sichuan ba-sin[J].Nature,2008,454:509-510.
[7]Luo L Z.Dynamic models of thelitho spheric evolution of the Longmenshan orogenic belt[J].Bulletin of Geological Insti-tute of Chengdu,1991,18(1):1-7(in Chinese).
[8]Xu Z Q,Hou L W,Wang Z X,et al.Processes of Mountain Building of the Songpan Ganzi Orogenic Belt in China[M].Beijing:Geological Publishing House,1992:73-87(in Chi-nese).
[9]Xu Z Q,Yang J S,Jiang M,et al.Continental subduction and uplifting of the orogenic belts at the margin of the Qing-hai-Tibetan Plateau[J].Earth Science Frontiers,1999,6(3):139-151(in Chinese).
[10]Deng Q D,Chen S F,Zhao X L,et al.Tectonics seismicity and dynamics of Longmenshan Mountains andits adjacent re-gions[J].Seismology and Geology,1994,16(4):389-402(in Chinese).
[11]Li Y,Zhou RJ,Densmore A L,et al.Continental Dynamic Processes and Geological Response in the Eastern Margin of the Qinghai-Tibet Plateau[M].Beijing:Geological Publish-ing House,2006:1-134(in Chinese).
[12]Burchfiel B C,Chen Z,Liu Y,et al.Tectonics of the Long-men Shan and adjacent regions[J].Int Geol Rev,1995,37:661-735.
[13]Zhao X L,Deng Q D,Chen S F.Tectonic geomorphology of the middle segment of the Longmenshanthrust fault zone[J].Seismology and Geology,1994,16(4):422-428(in Chi-nese).
[14]Ma B Q,Su G,Hou Z H,et al.Late Quaternary slip ratein the central part of the Longmengshan Fault zone fromterrace deformation along the Minjiang River[J].Seismology and Geology,2005,27(2):234-242(in Chinese).
[15]Densmore A L,Ellis MA,Yong Li,et al.Active tectonic of the Beichuan and Pengguanfaults at the eastern margin of the Tibetan Plateau[J].Tectonics,2007,26:TC4005,doi:10.1209/2006TC001987.
[16]Tang R C,Han WB.Active Faults and Earthquakes in Si-chuan Province[M].Beijing:Seismological Press,1993(in Chinese).
[17]Ding G Y,Tian QJ,Kong F C,et al.Segmentation of Ac-tive Fault:Principle,Method and Application[M].Beijing:Seismological Press,1993(in Chinese).
[18]Chen Y G,Chen W S,Lee J C,et al.Surface rupture of1999Chi-Chi earthquake yields insights on active tectonics of central Tai wan[J].Bull Seism Soc Am,2001,91(5):977-985.
[19]Kaneda H,Nakata T,Tsutsumi H,et al.Surface rupture of the2005Kashmir,Pakistan,earthquake and its active tec-tonicimplications[J].Bull SeismSoc Am,2008,98(2):521-557.
[20]Wan T F.The progress of researches on tectonic stress field[J].Earth Science Frontiers,1995,2(2):226-235(in Chi-nese).
[21]Doblas M,Mahecha V,Hoyos M,et al.Slickenside and fault surface kinematic indicators on active normal faults of the Alpine Betic cordilleras,Granada,Southern Spain[J].J Struct Geol,1997,19:159-170.
[22]Doblas M.Slickenside kinematicindicators[J].Tectonophys-ics,1998,295:187-197.
[23]Xu X W,Wen X Z,Ye J Q,et al.TheMs8.0Wenchuan earthquake surface ruptures andits seismogenic structure[J].Seismology and Geology,2008,30(3):597-629(in Chi-nese).
[1]中国地震台网中心.四川汶川县Ms8.0地震参数[OL/R].[2008-08-20].http:∥219.143.71.221/manage/fastReport.jsp-id=8a85532219b131b40119dba5e2c7011b.
[3]陈运泰,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[OL/R].[2008-08-20].http:∥www.csi.ac.cn/sichuan/chenyuntai.pdf.
[4]王卫民,赵连锋,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.
[7]罗立志.龙门山造山带岩石圈演化的动力学模式[J].成都地质学院学报,1991,18(1):1-7.
[8]许志琴,侯立玮,王宗秀,等.中国松潘甘孜造山带的造山过程[M].北京:地质出版社,1992:73-87.
[9]许志琴,杨经绥,姜枚,等.大陆俯冲作用及青藏高原周缘造山带的崛起[J].地学前缘,1999,6(3):139-151.
[10]邓起东,陈社发,赵小麟,等.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):389-402.
[11]李勇,周荣军,Densmore A L,等.青藏高原东缘大陆动力学过程与地质响应[M].北京:地质出版社,2006:1-134.
[13]赵小麟,邓起东,陈社发.龙门山逆断裂带中段的构造地貌学研究[J].地震地质,1994,16(4):422-428.
[14]马保起,苏刚,侯治华,等.利用岷江阶地的变形估算龙门山断裂带中段晚第四纪滑动速率[J].地震地质,2005,27(2):234-242.
[16]唐荣昌,韩渭宾.四川活动断裂与地震[M].北京:地震出版社,1993.
[17]丁国瑜,田勤俭,孔凡臣,等.活断层分段:原则、方法及应用[M].北京:地震出版社,1993.
[20]万天丰.构造应力场研究的新进展[J].地学前缘,1995,2(2):226-235.
[23]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.
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