汶川地震的地表破裂与逆冲-走滑作用
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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。作者以地表破裂为切入点,在映秀-北川断裂和彭灌断裂的关键部位,对断错山脊、洪积扇、河流阶地、边坡脊、断层陡坎、河道错断、冲沟侧缘壁位错、小路位错、公路位错、公路拱曲、构造裂缝、断层偏转、擦痕、挤压脊、坡中槽等汶川地震所导致的地表破裂和断裂带开展了详细的野外地貌测量,标定了映秀-北川断裂带和彭灌断裂的垂向断距和水平断距,结果表明汶川地震的地表破裂带沿北东东向延伸,走向介于NE30°~50°之间,倾向北西,倾角介于30°~40°之间。其中北川-映秀断裂带的破裂带从映秀向北东延伸达180~190 km,属于单侧多点破裂型,以逆冲-右行走滑为特点,垂直位错为1.60~6.00 m,水平位错为0.20~6.50 m;彭灌断裂的地表破裂出露于彭州磁峰场-绵竹汉旺之间,长度为30~40 km,以逆冲-右行走滑为特点,垂直位错为0.39~2.00 m之间,水平位错为0.20~0.70 m。表明该地震地表破裂带存在逆冲运动分量和右行走滑运动分量,逆冲运动分量略大于或等于右行走滑运动分量。根据历史地震和活动构造地貌的年龄测定资料,作者认为该区单条断裂的强震复发间隔在1~3ka。在此基础上,初步编制了龙门山地区的地质动力模型图,并认为下地壳物质在龙门山的近垂向挤出和垂向运动,导致了龙门山断裂带的向东逆冲运动、龙门山构造带抬升和汶川特大地震。
The Ms.8.0 huge earthquake of May 12th,2008 occurred in Yingxiu-Beichuan fault of Longmen Mountains belongs to a thrusted-strike-slip type.By laying emphasis on the geomorphic features of the surface ruptures of the huge earthquake in Longmen Mountains on the eastern margin of Qinghai-Tibet Plateau,this paper confirms the vertical and horizontal offsets of the Yingxiu-Beichuan fault and the Pengxian-Guanxian fault by detailed field geomorphic surveys.The authors have measured surface ruptures and cracks,such as terrace offset,scarp,fault-controlled saddles,dextral shutter ridges,dextral channel offsets,graben,shatter belt,fluvial fans offset,highroad offsets,tectonic cracks,press ridges and slope trench in some key positions.The result indicate that the surface rupture of the Wenchuan earthquake stretches to NEE direction which strikes NE 30°~50°and trends NE with a dip angle 30°~40°.The surface rupture of the Yingxiu-Beichuan fault stretches 180~190 km from Yingxiu to NE.It belongs to a single side-multi-dots type characterized by some dextral strike-slip thrusts with steep dip angles of 1.60~6.00 m vertical offsets and 0.20~6.50 m horizontal offsets.And the surface rupture of the Pengxian-Guanxian fault can be observed between Cifengchang of Pengzhou and Hanwang of Mianzhu.It is 30~40 km long and has some dextral strike-slip thrusts with slight dip angles of 0.39~2.00 m vertical offsets and 0.20~0.70 m horizontal offsets.These evidences indicate that the surface ruptures are thrusts with dextral strike-slip and thrust displacements.The thrust displacement are equal to or slightly bigger than the dextral strike-slip displacements.According to the historical earthquakes and active tectonic geomorphic dating data,the authors think that there has been and wil be a strong earthquake every 1~3 ka at this fault.Based on this,the authors set a dynamical model to illustrate the possible links between surface processes and upward extrusion of lower crustal flow on the eastern margin of the Qinghai-Tibet Plateau and conclude that the vertical press and motions of lower crust materials result in the thrust motions of the Longmen faulted zone to east,the tectonic uplift of Longmen Mountains and the huge Wenchuan earthquake.
The Ms.8.0 huge earthquake of May 12th,2008 occurred in Yingxiu-Beichuan fault of Longmen Mountains belongs to a thrusted-strike-slip type.By laying emphasis on the geomorphic features of the surface ruptures of the huge earthquake in Longmen Mountains on the eastern margin of Qinghai-Tibet Plateau,this paper confirms the vertical and horizontal offsets of the Yingxiu-Beichuan fault and the Pengxian-Guanxian fault by detailed field geomorphic surveys.The authors have measured surface ruptures and cracks,such as terrace offset,scarp,fault-controlled saddles,dextral shutter ridges,dextral channel offsets,graben,shatter belt,fluvial fans offset,highroad offsets,tectonic cracks,press ridges and slope trench in some key positions.The result indicate that the surface rupture of the Wenchuan earthquake stretches to NEE direction which strikes NE 30°~50°and trends NE with a dip angle 30°~40°.The surface rupture of the Yingxiu-Beichuan fault stretches 180~190 km from Yingxiu to NE.It belongs to a single side-multi-dots type characterized by some dextral strike-slip thrusts with steep dip angles of 1.60~6.00 m vertical offsets and 0.20~6.50 m horizontal offsets.And the surface rupture of the Pengxian-Guanxian fault can be observed between Cifengchang of Pengzhou and Hanwang of Mianzhu.It is 30~40 km long and has some dextral strike-slip thrusts with slight dip angles of 0.39~2.00 m vertical offsets and 0.20~0.70 m horizontal offsets.These evidences indicate that the surface ruptures are thrusts with dextral strike-slip and thrust displacements.The thrust displacement are equal to or slightly bigger than the dextral strike-slip displacements.According to the historical earthquakes and active tectonic geomorphic dating data,the authors think that there has been and wil be a strong earthquake every 1~3 ka at this fault.Based on this,the authors set a dynamical model to illustrate the possible links between surface processes and upward extrusion of lower crustal flow on the eastern margin of the Qinghai-Tibet Plateau and conclude that the vertical press and motions of lower crust materials result in the thrust motions of the Longmen faulted zone to east,the tectonic uplift of Longmen Mountains and the huge Wenchuan earthquake.
引文
[1]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.
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[8]LI Yong,DENSMORE A L,ALLEN P A.et al.Sedimentary responses to thrusting and strike-slipping of Longmen Shan along eastern margin ofTibetan Plateau,and their implication of Cimmeriancontinents and India/Eurasia collision[J].ScientiaGeologica Sinica,2001,10(4):223-243.
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[11]RICHARDSON N,DENSMORE A L,SEWARDD,et al.Extraordinary denudation in the SichuanBasin:Insights from low-temperature thermochro-nology adjacent to the eastern margin of the TibetanPlateau[J].J Geophys Res,2007,113,B04409,doi:10.1029/2006JB004739.
[12]ROYDEN L H,BURCHFIEL B C,KING R W,etal.Surface deformation and lower crustal flow ineastern Tibet[J].Science,1997,276:788-790.
[13]SCHLUNEGGER F,MELZER J,CLARK M K,etal.Topographic ooze:Building the eastern marginof Tibet by lower crustal flow[J].Geology,2000,28:703-706.
[14]CHEN Z,BUCHIFIEL B C,LIU Y,et al.Globalpositioning system measurements from eastern Tibetand their implication for India/Eurasia intercontinen-tal deformation[J].J Geophys Res,2000,105:16215-16228
[15]ZHANG P Z,SHEN Z,WANG M,et al.Continu-ous deformation of the Tibetan Plateau from globalpositioning system data[J].Geology,2004,32:809-812.
[16]LI Yong,ELLIS M A,DENSMORE A L,et al.Active Tectonics in the Longmen Shan Region,East-ern Tibetan Plateau[J].EOS Transactions of theAmerican Geophysical Union,2001,81(48):1109.
[17]LI Yong,ELLIS M A,DENSMORE A L,et al.Evidence for active strike-slip faults in the LongmenShan,Eastern margin of Tibet[J].EOS Transac-tions of the American Geophysical Union,2000,82(47):1104.
[18]李勇,周荣军,DENSMORE A L,等.青藏高原东缘龙门山晚新生代走滑-逆冲作用的地貌标志[J].第四纪研究,2006,26(1):40-51.
[19]李勇,周荣军,DENSMORE A L,等.青藏高原东缘龙门山晚新生代走滑挤压作用的沉积响应[J].沉积学报,2006,24(2):1-12.
[20]邓起东,于贵军,叶文华.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)[M].北京:地震出版社,1992.
[21]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[DB/OL].http://www.csi.ac.cn,
[22]中国地质调查局发展研究中心情报室.科学家提出汶川地震两阶段模式[DB/OL].http://www.cgs.gov.cn
[23]ENGLAND P C,MOLNAR P.Right-lateral shearand rotation as the explanation for strike-slip faul-ting in eastern Tibet[J].Nature,1990,344:140-142.
[24]AVOUAC J P,TAPPONNIER P.Kinematic modelof active deformation in central Asia[J].Geophysi-cal Research Letters,1993,20:895-898.
[25]CLARK M K,ROYDEN L H,WHIPPLE K X,etal.Use of a regional,relict landscape to measurevertical deformation of the eastern Tibetan Plateau[J].J Geophys Res,2006,111,F03002,doi:10.1029/2005JF000294.
[26]CLARK M K,HOUSE M A,ROYDEN L H,etal.Late Cenozoic uplift of southeastern Tibet[J].Geology,2005,33:525-528.
[27]MENG Qing-Ren,HU Jian-Min,WANG E,et al.Late Cenozoic denudation by large-magnitude land-slides in the eastern edge of Tibetan Plateau[J].EPSL,2006,243:252-267.
[28]李勇,徐公达,周荣军,等.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[J].地质通报,2005,24(12):1162-1169.
[2]LI Yong,ZHOU Rongjun,DENSMORE A L,et al.The Geology of the Eastern Margin of the Qinghai-Tibet Plateau[M].北京:地质出版社,2006.
[3]周荣军,李勇,DENSMORE A L,,等.青藏高原东缘活动构造[J].矿物岩石,2006,26(2):40-51.
[4]DENSMORE A L,ELLIS M A,LI Yong,et al.Active tectonics of the Beichuan and Pengguan faultsat the eastern margin of the Tibetan Plateau[J].Tec-tonics,2007,80(8):113-127.
[5]刘树根.龙门山冲断带与川西前陆盆地形成演化[M].成都:成都科技大学出版社,1993:17-117.
[6]李勇,曾允孚,伊海生.龙门山前陆盆地沉积及构造演化[M].成都:成都科技大学出版社,1995:1-91.
[7]DENSMORE A L,LI Yong,ELLIS M,et al.Activetectonics and erosional unloading of eastern margin[J].Journal of Mountain Science,2005,2(2):146-154.
[8]LI Yong,DENSMORE A L,ALLEN P A.et al.Sedimentary responses to thrusting and strike-slipping of Longmen Shan along eastern margin ofTibetan Plateau,and their implication of Cimmeriancontinents and India/Eurasia collision[J].ScientiaGeologica Sinica,2001,10(4):223-243.
[9]LI Y,ALLEN P A,DENSMORE A L,et al.Evolu-tion of the Longmen Shan Foreland Basin(westernSichuan,China)during the Late Triassic IndosinianOrogeny[J].Basin Res,2003,15:117-138.
[10]李勇,周荣军,DENSMORE A L,等.龙门山断裂带走滑方向的反转及其沉积与地貌标志[J].矿物岩石,2006,26(4):26-34.
[11]RICHARDSON N,DENSMORE A L,SEWARDD,et al.Extraordinary denudation in the SichuanBasin:Insights from low-temperature thermochro-nology adjacent to the eastern margin of the TibetanPlateau[J].J Geophys Res,2007,113,B04409,doi:10.1029/2006JB004739.
[12]ROYDEN L H,BURCHFIEL B C,KING R W,etal.Surface deformation and lower crustal flow ineastern Tibet[J].Science,1997,276:788-790.
[13]SCHLUNEGGER F,MELZER J,CLARK M K,etal.Topographic ooze:Building the eastern marginof Tibet by lower crustal flow[J].Geology,2000,28:703-706.
[14]CHEN Z,BUCHIFIEL B C,LIU Y,et al.Globalpositioning system measurements from eastern Tibetand their implication for India/Eurasia intercontinen-tal deformation[J].J Geophys Res,2000,105:16215-16228
[15]ZHANG P Z,SHEN Z,WANG M,et al.Continu-ous deformation of the Tibetan Plateau from globalpositioning system data[J].Geology,2004,32:809-812.
[16]LI Yong,ELLIS M A,DENSMORE A L,et al.Active Tectonics in the Longmen Shan Region,East-ern Tibetan Plateau[J].EOS Transactions of theAmerican Geophysical Union,2001,81(48):1109.
[17]LI Yong,ELLIS M A,DENSMORE A L,et al.Evidence for active strike-slip faults in the LongmenShan,Eastern margin of Tibet[J].EOS Transac-tions of the American Geophysical Union,2000,82(47):1104.
[18]李勇,周荣军,DENSMORE A L,等.青藏高原东缘龙门山晚新生代走滑-逆冲作用的地貌标志[J].第四纪研究,2006,26(1):40-51.
[19]李勇,周荣军,DENSMORE A L,等.青藏高原东缘龙门山晚新生代走滑挤压作用的沉积响应[J].沉积学报,2006,24(2):1-12.
[20]邓起东,于贵军,叶文华.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)[M].北京:地震出版社,1992.
[21]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[DB/OL].http://www.csi.ac.cn,
[22]中国地质调查局发展研究中心情报室.科学家提出汶川地震两阶段模式[DB/OL].http://www.cgs.gov.cn
[23]ENGLAND P C,MOLNAR P.Right-lateral shearand rotation as the explanation for strike-slip faul-ting in eastern Tibet[J].Nature,1990,344:140-142.
[24]AVOUAC J P,TAPPONNIER P.Kinematic modelof active deformation in central Asia[J].Geophysi-cal Research Letters,1993,20:895-898.
[25]CLARK M K,ROYDEN L H,WHIPPLE K X,etal.Use of a regional,relict landscape to measurevertical deformation of the eastern Tibetan Plateau[J].J Geophys Res,2006,111,F03002,doi:10.1029/2005JF000294.
[26]CLARK M K,HOUSE M A,ROYDEN L H,etal.Late Cenozoic uplift of southeastern Tibet[J].Geology,2005,33:525-528.
[27]MENG Qing-Ren,HU Jian-Min,WANG E,et al.Late Cenozoic denudation by large-magnitude land-slides in the eastern edge of Tibetan Plateau[J].EPSL,2006,243:252-267.
[28]李勇,徐公达,周荣军,等.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[J].地质通报,2005,24(12):1162-1169.
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