汶川8级大地震的地表破裂特征及分段
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摘要
2008年5月12日14时28分,四川省汶川县境内发生MS8.0地震。地表破裂多以跌水、陡坎形态发育在河流沟谷或晚新生代沉积层内,位移明显。山地受崩塌、滑坡影响,位移量较难获得。发震断裂主要有三条,即北川-映秀断裂、彭县-灌县断裂和小鱼洞断裂。北川-映秀断裂地表破裂由南向北活动性质从逆冲为主逐渐转变为走滑为主,长约220 km,平均垂直位移量约3 m,按位移量沿断裂走向的变化可以分为虹口段、北川段和南坝段;彭县-灌县断裂地表破裂以逆冲活动为主,长约82 km,平均垂直位移量约1.5 m,可以划分为白鹿段和汉旺段,断裂断距分布的几何特征与北川-映秀断裂的中南段相近;小鱼洞断裂是一条新生北西走向的次级破裂,长约5.6 km,平均垂直位移量约1.5 m,调节两侧构造单元变形差异,具有捩断层特征,活动以逆(左行)走滑为主,可划分出小鱼洞段和中坝段。姚都镇地表破裂可能说明南坝以北的地震具有不同的活动特征。活动断裂的运动方式反映区域应力场有北西西向挤压特征。
Detailed field investigation showed that three seismogenic faults ruptured in the Wenchuan MS8.0 earthquake,which are Beichuan-Yinxiu fault,Penxian-Guanxian fault,and Xiaoyudong fault.The Beichuan-Yinxiu fault is characterized by reverse faulting in the south and right-lateral faulting in the north,which lasted for 220 km long and vertically displaced 3 meters on average,and can be divided into three segments.The Penxian-Guanxian fault rupture is characterized by reverse faulting which is 5.6 km long and vertically displaced 1.5 meters on average,and can be divided into two segments.Xiaoyudong secondary fault is characterized by tear faulting and was formed in this earthquake,left-laterally faulted 5.6 km long with 1.5 m vertical displacement on average,which accommodated the different deformations of tectonic units on both side.The surface rupture on Yaodu town may show the different characteristics between Nanba segment and Beichuan segment.The geometry and motion mode indicate that the maximum horizontal main stress in this region is in the direction of NWW.
Detailed field investigation showed that three seismogenic faults ruptured in the Wenchuan MS8.0 earthquake,which are Beichuan-Yinxiu fault,Penxian-Guanxian fault,and Xiaoyudong fault.The Beichuan-Yinxiu fault is characterized by reverse faulting in the south and right-lateral faulting in the north,which lasted for 220 km long and vertically displaced 3 meters on average,and can be divided into three segments.The Penxian-Guanxian fault rupture is characterized by reverse faulting which is 5.6 km long and vertically displaced 1.5 meters on average,and can be divided into two segments.Xiaoyudong secondary fault is characterized by tear faulting and was formed in this earthquake,left-laterally faulted 5.6 km long with 1.5 m vertical displacement on average,which accommodated the different deformations of tectonic units on both side.The surface rupture on Yaodu town may show the different characteristics between Nanba segment and Beichuan segment.The geometry and motion mode indicate that the maximum horizontal main stress in this region is in the direction of NWW.
引文
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[21]张军龙,田勤俭,李智敏,等.差分GPS方法在城市活断层探测中的应用探讨[J].地震,2007,27(3):74-82.
[22]张军龙,田勤俭,李峰,等.海南岛北西部新构造特征及其演化研究[J].地震,2008,28(3):85-95.
[23]张军龙,田勤俭,张小龙,等.DGPS方法在新构造研究中的应用探讨[J].地学前缘,2008,15(4):290-297.
[2]USGS.2008.Magnitude 7.9-Eastern Sichuan,China[R].http://earthquake.usgs.gov/eqcenter/eqinthenews/2008/us2008ryan/.
[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[R].2008.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):1 403-1 410.
[5]Ji C,Hayes G.2008.Preliminary result of the May 12,2008MW7.9 Eastern Sichuan,China Earth-quake[R].http://earthquake.usgs.gov/eqcenter/eqinthenews/2008/us2008ryan/finite_fault.php
[6]Parsons T,Ji C,Kirby E.Stress changes from the 2008 Wenchuan earthquake and increased hazardin the Sichuan basin,NATURE,2008,454(7203),509-510.
[7]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.
[8]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.
[9]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.
[10]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.
[11]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.
[12]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.
[13]唐荣昌,韩渭宾.四川活动断裂与地震[M].北京:地震出版社,1993.
[14]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[A].北京:地质出版社,2006.1-134.
[15]Burchfiel B C,Chen Z,Liu Y,et al.Tectonics of the Longmen Shan and adjacent regions[J].IntGeol Rev,1995,37:661-735.
[16]李传友,宋方敏,冉勇康.龙门山断裂带北段晚第四纪活动性讨论[J].地震地质,2004,26(2):248-258.
[17]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.
[18]Densmore A L,Ellis M A,Yong Li,et al.Active tectonic of the Beichuan and Pengguan faults atthe eastern margin of the Tibetan Plateau[J].Tectonics,2007,26,TC4005,doi:10.1209/2006TC001987.
[19]杨晓平,蒋溥,宋方敏,等.龙门山断裂带南段错断晚更新世以来地层的证据[J].地震地质,1999,21(4):341-345.
[20]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.
[21]张军龙,田勤俭,李智敏,等.差分GPS方法在城市活断层探测中的应用探讨[J].地震,2007,27(3):74-82.
[22]张军龙,田勤俭,李峰,等.海南岛北西部新构造特征及其演化研究[J].地震,2008,28(3):85-95.
[23]张军龙,田勤俭,张小龙,等.DGPS方法在新构造研究中的应用探讨[J].地学前缘,2008,15(4):290-297.
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