映秀-北川断裂的地表破裂与变形特征
摘要
2008年5月12日在龙门山映秀-北川断裂带发生的8.0级特大地震,属于逆冲—走滑型地震。本文以地表破裂为切入点,在映秀-北川断裂的关键部位开展了详细的野外地貌测量,标定了映秀-北川断裂带的垂向断距和水平断距,结果表明映秀-北川断裂的地表破裂带从映秀向北东延伸达180～190km,走向介于NE30°～50°之间,倾向北西,地表平均垂向断距为2.9m,平均水平断距为3.1m;地表最大错动量的地点位于北川县擂鼓镇,垂直断错为6.2±0.1m,水平断错为6.8±0.2m,逆冲分量与右行走滑分量的比值为3∶1～1∶1,表明该断裂以逆冲—右行走滑为特点,逆冲运动分量略大于或等于右行走滑运动分量。根据近南北向的分段断裂可将映秀-北川断层的地表破裂带划分为两个高值区和两个低值区,其中两个高值区分别位于南段的映秀—虹口一带和中北段的擂鼓—北川县城—邓家坝一带。基于保存于破裂面上的擦痕,我们将该地震破裂过程划分为两个阶段,早期为逆冲作用,晚期为斜向走滑作用。
The MS 8.0 great earthquake of 12 May 2008 which occurred in the Yingxiu-Beichuan fault of Longmen Mountain belongs to strike-slip-type thrust. With an emphasis on the geomorphic features of the surface ruptures of the great earthquake in Longmen Mountain, the eastern margin of Tibetan Plateau, this paper defines the vertical and horizontal offsets of the Yingxiu-Beichuan fault by detail field geomorphic surveys. The results show that the surface rupture of the Yingxiu-Beichuan fault stretches to NEE direction (NE30°~50°) for 180~190 km from Yingxiu to the surface rupture of Beichuan. The average vertical and horizontal offsets are 2.9 m and 3.1 m, respectively, with the largest vertical and horizontal offsets of 6.2±0.1 m and 6.8±0.2 m in Leigu town. The ratio of thrusting and dextral slipping in the Yingxiu-Beichuan is 3∶1~1∶1, indicating that the surface ruptures are characterized with thrusting displacement slightly more than or equal to dextral strike-slip one. Based on the nearly NS-trending fault, the surface rupture of the Yingxiu-Beichuan fault can be divided into two segments of large rupture and two segments of small rupture, with the former located at the southern section (Hongkou) and middle section (Leigu) of Yingxiu, Chuanbei county, and Dengjiaba area. We divide the process of seismic rupture into two stages based on the scratch preserved on the fracture planes: early thrusting and later oblique slip motion.
The MS 8.0 great earthquake of 12 May 2008 which occurred in the Yingxiu-Beichuan fault of Longmen Mountain belongs to strike-slip-type thrust. With an emphasis on the geomorphic features of the surface ruptures of the great earthquake in Longmen Mountain, the eastern margin of Tibetan Plateau, this paper defines the vertical and horizontal offsets of the Yingxiu-Beichuan fault by detail field geomorphic surveys. The results show that the surface rupture of the Yingxiu-Beichuan fault stretches to NEE direction (NE30°~50°) for 180~190 km from Yingxiu to the surface rupture of Beichuan. The average vertical and horizontal offsets are 2.9 m and 3.1 m, respectively, with the largest vertical and horizontal offsets of 6.2±0.1 m and 6.8±0.2 m in Leigu town. The ratio of thrusting and dextral slipping in the Yingxiu-Beichuan is 3∶1~1∶1, indicating that the surface ruptures are characterized with thrusting displacement slightly more than or equal to dextral strike-slip one. Based on the nearly NS-trending fault, the surface rupture of the Yingxiu-Beichuan fault can be divided into two segments of large rupture and two segments of small rupture, with the former located at the southern section (Hongkou) and middle section (Leigu) of Yingxiu, Chuanbei county, and Dengjiaba area. We divide the process of seismic rupture into two stages based on the scratch preserved on the fracture planes: early thrusting and later oblique slip motion.
引文
陈运泰,许力生,张勇,等.2008.2008年5月12日汶川特大地震震源特性分析报告,http://www.csi.ac.cn.
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李勇,周荣军,Densmore A L,等.2006.青藏高原东缘大陆动力学过程与地质响应.北京:地质出版社.
李勇,周荣军,Densmore A L,等.2006.龙门山断裂带走滑方向的反转及其沉积与地貌标志.矿物岩石,26(4):26~34.
李勇,周荣军,Densmore A L,等.2006.青藏高原东缘龙门山晚新生代走滑—逆冲作用的地貌标志.第四纪研究26(1):40~51.
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李勇,周荣军,董顺利,等.2008.汶川特大地震的地表破裂与逆冲-走滑作用.成都理工大学学报(自然科学版),35(4):404~413.
刘树根.1993.龙门山冲断带与川西前陆盆地形成演化.成都:成都科技大学出版社,17~117.
中国地质调查局发展研究中心情报室.2008.科学家提出汶川地震两阶段模式.http://www.cgs.gov.cn.
周荣军,李勇,Densmore A L,等.2006.青藏高原东缘活动构造.矿物岩石,26(2):40~51.
Avouac J P,Tapponnier P.1993.Kinematic model of activedeformationin central Asia.Geophysical Research Letters,20:895~898.
Chen Z,B C Buchifiel,Y Liu,R,et al.2000.Global positioningsystem measurements from eastern Tibet and their i mplicationfor India/Eurasiaintercontinental deformation.J.geophys.Res,105:16215~16228.
Clark MK,L HRoyden,K X Whipple,B C Burchfiel,XZhang,WTang.2006.Use of a regional,relict landscape to measurevertical deformation of the eastern Tibetan Plateau,J.Geophys.Res.,111,F03002,doi:10.1029/2005JF000294.
Clark M K,M A House,L H Royden,K X et al.2005.LateCenozoic uplift of southeastern Tibet,Geology,33,525~528.
Densmore A L,Ellis M A,Li Yong et al.2007.Active tectonics ofthe Beichuan and Pengguan faults at the eastern margin of theTibetan Plateau.Tectonics,80(8):113~127.
Densmore,A L,Li Yong,Michael Ellis et al.2005.Active tectonicsand erosional unloading of eastern margin.Journal of MountainScience,2(2):146~154.
England P C,Molnar P.1990.Right-lateral shear and rotation asthe explanationfor strike-slipfaultingin eastern.Tibet.Nature,344:140~142.
Li Y,Allen P A,Densmore A L.et al.2003.Evolution of theLongmen Shan Foreland Basin(western Sichuan,China)duringthe Late Triassic Indosinian Orogeny.Basin Res,15:117~138.
Li Yong,Densmore A L,Allen P A,et al.2001.Sedi mentaryresponses to thrusting and strike-slipping of Longmen Shanalong eastern margin of Tibetan Plateau,andtheir i mplication ofCi mmerian continents and India/Eurasia collision.Scientia.Geologica Sinica,10(4):223~243.
Li Yong,Ellis M A,Densmore A L.et al.2001.Active Tectonics inthe Longmen Shan Region,Eastern Tibetan Plateau,EOSTransactions of the American Geophysical Union,81(48):1109.
Li Yong,Ellis M A,Densmore A L.et al.2000.Evidence for activestrike-slipfaultsinthe Longmen Shan,Eastern margin of Tibet.EOS Transactions of the American Geophysical Union,82(47):1104.
Li Yong,Zhou Rongjun,Densmore A L et al.2006.The Geology ofthe Eastern Magin of the Qinghai-Tiben Plateau.北京:地质出版社。
Li Yong,Zhou Rongjun,Alexander L.Densmore et al.2008.Surfacerupture,thrusting and strike-slipping in the WenchuanEarthquake.The Gongwana13Program and Abstracts:114~115.
Meng,Qing Ren,Jian Min Hu,Erchie Wang et al.2006.Late Cenozoic denudation by large-magnitude landslides in theeastern edge of Tibetan Plateau.EPSL,243:252~267.
Richardson N,A L Densmore,D Seward,A et al.2007.Extraordinary denudation in the Sichuan Basin:Insights fromlow-temperature thermochronology adjacent to the easternmargin of the Tibetan Plateau,J.Geophys.Res.,113,B04409,doi:10.1029/2006JB004739.
Royden,L H,B C Burchfiel,R W King,et al.1997.Surface deformation and lower crustal flow in eastern Tibet,Science,276:788~790.
Schlunegger F,J Melzer,Clark M K et al.Topographic ooze:Building the eastern margin of Tibet by lower crustal flow,Geology,28,703~706.
Zhang P Z,Z Shen,M Wang,W J,et al.2004.Continuousdeformation of the Tibetan Plateau from global positioningsystemdata.Geology,32:809~812.
邓起东,于贵军,叶文华.1992.地震地表破裂参数与震级关系研究,活动断裂研究理论与应用(2).地震出版社.
李勇,曾允孚,伊海生.1995.龙门山前陆盆地沉积及构造演化.成都:成都科技大学出版社,1~91.
李勇,徐公达,周荣军,等.2005.龙门山均衡重力异常及其对青藏高原东缘山脉地壳隆升的约束.地质通报,24(12):1162~1169.
李勇,周荣军,Densmore A L,等.2006.青藏高原东缘大陆动力学过程与地质响应.北京:地质出版社.
李勇,周荣军,Densmore A L,等.2006.龙门山断裂带走滑方向的反转及其沉积与地貌标志.矿物岩石,26(4):26~34.
李勇,周荣军,Densmore A L,等.2006.青藏高原东缘龙门山晚新生代走滑—逆冲作用的地貌标志.第四纪研究26(1):40~51.
李勇,周荣军,Densmore A L,等.2006.青藏高原东缘龙门山晚新生代走滑挤压作用的沉积响应.沉积学报,24(2):1~12.
李勇,周荣军,董顺利,等.2008.汶川特大地震的地表破裂与逆冲-走滑作用.成都理工大学学报(自然科学版),35(4):404~413.
刘树根.1993.龙门山冲断带与川西前陆盆地形成演化.成都:成都科技大学出版社,17~117.
中国地质调查局发展研究中心情报室.2008.科学家提出汶川地震两阶段模式.http://www.cgs.gov.cn.
周荣军,李勇,Densmore A L,等.2006.青藏高原东缘活动构造.矿物岩石,26(2):40~51.
Avouac J P,Tapponnier P.1993.Kinematic model of activedeformationin central Asia.Geophysical Research Letters,20:895~898.
Chen Z,B C Buchifiel,Y Liu,R,et al.2000.Global positioningsystem measurements from eastern Tibet and their i mplicationfor India/Eurasiaintercontinental deformation.J.geophys.Res,105:16215~16228.
Clark MK,L HRoyden,K X Whipple,B C Burchfiel,XZhang,WTang.2006.Use of a regional,relict landscape to measurevertical deformation of the eastern Tibetan Plateau,J.Geophys.Res.,111,F03002,doi:10.1029/2005JF000294.
Clark M K,M A House,L H Royden,K X et al.2005.LateCenozoic uplift of southeastern Tibet,Geology,33,525~528.
Densmore A L,Ellis M A,Li Yong et al.2007.Active tectonics ofthe Beichuan and Pengguan faults at the eastern margin of theTibetan Plateau.Tectonics,80(8):113~127.
Densmore,A L,Li Yong,Michael Ellis et al.2005.Active tectonicsand erosional unloading of eastern margin.Journal of MountainScience,2(2):146~154.
England P C,Molnar P.1990.Right-lateral shear and rotation asthe explanationfor strike-slipfaultingin eastern.Tibet.Nature,344:140~142.
Li Y,Allen P A,Densmore A L.et al.2003.Evolution of theLongmen Shan Foreland Basin(western Sichuan,China)duringthe Late Triassic Indosinian Orogeny.Basin Res,15:117~138.
Li Yong,Densmore A L,Allen P A,et al.2001.Sedi mentaryresponses to thrusting and strike-slipping of Longmen Shanalong eastern margin of Tibetan Plateau,andtheir i mplication ofCi mmerian continents and India/Eurasia collision.Scientia.Geologica Sinica,10(4):223~243.
Li Yong,Ellis M A,Densmore A L.et al.2001.Active Tectonics inthe Longmen Shan Region,Eastern Tibetan Plateau,EOSTransactions of the American Geophysical Union,81(48):1109.
Li Yong,Ellis M A,Densmore A L.et al.2000.Evidence for activestrike-slipfaultsinthe Longmen Shan,Eastern margin of Tibet.EOS Transactions of the American Geophysical Union,82(47):1104.
Li Yong,Zhou Rongjun,Densmore A L et al.2006.The Geology ofthe Eastern Magin of the Qinghai-Tiben Plateau.北京:地质出版社。
Li Yong,Zhou Rongjun,Alexander L.Densmore et al.2008.Surfacerupture,thrusting and strike-slipping in the WenchuanEarthquake.The Gongwana13Program and Abstracts:114~115.
Meng,Qing Ren,Jian Min Hu,Erchie Wang et al.2006.Late Cenozoic denudation by large-magnitude landslides in theeastern edge of Tibetan Plateau.EPSL,243:252~267.
Richardson N,A L Densmore,D Seward,A et al.2007.Extraordinary denudation in the Sichuan Basin:Insights fromlow-temperature thermochronology adjacent to the easternmargin of the Tibetan Plateau,J.Geophys.Res.,113,B04409,doi:10.1029/2006JB004739.
Royden,L H,B C Burchfiel,R W King,et al.1997.Surface deformation and lower crustal flow in eastern Tibet,Science,276:788~790.
Schlunegger F,J Melzer,Clark M K et al.Topographic ooze:Building the eastern margin of Tibet by lower crustal flow,Geology,28,703~706.
Zhang P Z,Z Shen,M Wang,W J,et al.2004.Continuousdeformation of the Tibetan Plateau from global positioningsystemdata.Geology,32:809~812.
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