2008年汶川地震中断坡-滑脱断层破裂:龙门山挤压隆升的大地测量证据
|
摘要
青藏高原东缘龙门山构造隆升一直存在挤压造山模式和下地壳层流模式之争.下地壳层流模型认为,龙门山隆升与水平缩短关系不大,山前断层只是高原、盆地间差异性垂直运动的结果,高原之下无需挤压模式中的大规模水平滑脱层.本文利用近场密集的同震形变数据,约束汶川地震破裂几何特征及同震滑动分布.反演结果显示汶川地震撕裂龙门山中南段近水平滑脱层,宽度达到60～80km,释放能量约占总标量地震矩的12%,在16～21km深度出现两三个滑动量高达6～7m的破裂区.深部低角度破裂往上转为高角度逆冲,沿龙门山中央断裂以约55°倾角出露地表.汶川地震破裂的几何产状和滑移幅度表明龙门山冲断带发育大规模的近水平滑脱层,是青藏高原东缘地壳缩短增厚、龙门山挤压隆升的重要证据.
The mechanism for the build-up of the Longmen Shan on the eastern margin of Tibet is controversial with two end-member models of crustal thickening -mid-crustal channel flow vs crustal shortening.The former states that the uplift of the Longmen Shan results from an eastward flowing of mid-lower crust from the interior of the Tibetan Plateau driven by the collision between India and Tibet.As a result,the thrust fault system on the foothill of the Longmen Shan was produced to accommodate differential vertical motions between eastern Tibet and Sichuan Basin,requiring no large-scale ramp-décollement structure associated with crustal shortening.In this study,we use dense near-field geodetic measurements of coseismic deformation to constrain rupture geometry and slip distribution of the Wenchuan earthquake.Our modelling shows a sub-horizontal décollement fault at depths of 16~21 km with a 60~80 km downdip width,on which there are several high-slip patches with peak values of 6~7 meters,altogether corresponding to 12% of total scalar geodetic moment.Deep slip with a dipping angle of 7° extends updip with rupturing on two high-angle ramp faults,one of which emerges at the surface as the Beichuan fault dipping about 55° to west.The great rupture on the ramp and décollement faults under the Longmen Shan provide evidence of the existence of a large-scale faulting system characterized with substantial crustal shearing at depth along a transition zone located between the upper brittle and the underlying ductile layers,suggesting that the crustal shortening across the eastern margin of the Tibetan Plateau gives rise to the growth of the Longmen Shan.
The mechanism for the build-up of the Longmen Shan on the eastern margin of Tibet is controversial with two end-member models of crustal thickening -mid-crustal channel flow vs crustal shortening.The former states that the uplift of the Longmen Shan results from an eastward flowing of mid-lower crust from the interior of the Tibetan Plateau driven by the collision between India and Tibet.As a result,the thrust fault system on the foothill of the Longmen Shan was produced to accommodate differential vertical motions between eastern Tibet and Sichuan Basin,requiring no large-scale ramp-décollement structure associated with crustal shortening.In this study,we use dense near-field geodetic measurements of coseismic deformation to constrain rupture geometry and slip distribution of the Wenchuan earthquake.Our modelling shows a sub-horizontal décollement fault at depths of 16~21 km with a 60~80 km downdip width,on which there are several high-slip patches with peak values of 6~7 meters,altogether corresponding to 12% of total scalar geodetic moment.Deep slip with a dipping angle of 7° extends updip with rupturing on two high-angle ramp faults,one of which emerges at the surface as the Beichuan fault dipping about 55° to west.The great rupture on the ramp and décollement faults under the Longmen Shan provide evidence of the existence of a large-scale faulting system characterized with substantial crustal shearing at depth along a transition zone located between the upper brittle and the underlying ductile layers,suggesting that the crustal shortening across the eastern margin of the Tibetan Plateau gives rise to the growth of the Longmen Shan.
引文
[1]Burchfiel B C,Chen Z L,Liu Y P,et al.Tectonics of theLongmen Shan and adjacent regions,central China.Int.Geol.Rev.,1995,37(8):661-735.
[2]Avouac J.Dynamic processes in extensional and compressionalsettings-mountain building:From earthquakes to geologicaldeformation.Treatise on Geophysics,2008,6:377-439.
[3]Shen Z K,Sun J B,Zhang P Z,et al.Slip maxima at faultjunctions and rupturing of barriers during the 2008Wenchuanearthquake.Nat.Geosci.,2009,2:718-724.
[4]闻学泽,张培震,杜方等.2008年汶川8.0级地震发生的历史与现今地震活动背景.地球物理学报,2009,52(2):444-454.Wen X Z,Zhang P Z,Du F,et al.The background ofhistorical and modern seismic activities of the occurrence ofthe 2008 Ms8.0Wenchuan,Sichuan,earthquake.Chinese J.Geophys.(in Chinese),2009,52(2):444-454.
[5]Royden L H,Burchfiel B C,King R W,et al.Surfacedeformation and lower crustal flow in eastern Tibet.Science,1997,276(5313):788-790.
[6]杨少敏,兰启贵,聂兆生等.用多种数据构建2008年汶川特大地震同震位移场.地球物理学报,2012,55(8):2575-2588.Yang S M,Lan Q G,Nie Z S,et al.Coseismic displacementcaused by the 2008great Wenchuan earthquake derived fromvarious types of geodetic data.Chinese J.Geophys.(inChinese),2012,55(8):2575-2588.
[7]孙建宝,梁芳,沈正康等.汶川Ms8.0地震InSAR形变观测及初步分析.地震地质,2008,30(3):789-795.Sun J B,Liang F,Shen Z K,et al.InSAR deformationobservation and preliminary analysis of the Ms8.0 Wenchuanearthquake.Seismology and Geology(in Chinese),2008,30(3):789-795.
[8]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.地球物理学报,2009,52(2):390-397.Chen J H,Liu Q Y,Li S C,et al.Seismotectonic study byrelocation of the Wenchuan Ms8.0 earthquake sequence.Chinese J.Geophys.(in Chinese),2009,52(2):390-397.
[9]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.地震地质,2008,30(3):597-629.Xu X W,Wen X Z,Ye J Q,et al.The Ms8.0 Wenchuanearthquake surface ruptures and its seismogenic structure.Seismology and Geology(in Chinese),2008,30(3):597-629.
[10]Wang Q,Qiao X J,Lan Q G,et al.Rupture of deep faults inthe 2008 Wenchuan earthquake and uplift of the LongmenShan.Nature Geosci.,2011,4:634-640.
[11]Okada Y.Surface deformation due to shear and tensile faultsin a half-space.Bull.Seismol.Soc.Am.,1985,75:1135-1154.
[12]王敏.基于GPS同震位移场约束反演2008年5.12汶川大地震破裂空间分布.地球物理学报,2009,52(10):2519-2526.Wang M.Coseismic slip distribution of the 2008 Wenchuangreat earthquake constrained using GPS coseismic displacementfield.Chinese J.Geophys.(in Chinese),2009,52(10):2519-2526.
[13]Feng G C,Hetland E A,Ding X L,et al.Coseismic faultslip of the 2008 Mw7.9Wenchuan earthquake estimated fromInSAR and GPS measurements.Geophys.Res.Lett.,2010,37(1):doi:10.1029/2009GL041213.
[14]Tong X P,Sandwell D T,Fialko Y R.Coseismic slip modelof the 2008Wenchuan earthquake derived from joint inversionof interferometric synthetic aperture radar,GPS,and fielddata.J.Geophys.Res.,2010,115(B4),doi:10.1029/2009JB006625.
[15]Xu C J,Liu Y,Wen Y M,et al.Coseismic slip distributionof the 2008 Mw7.9Wenchuan earthquake from joint inversionof GPS and InSAR data.Bull.Seism.Soc.Am.,2010,100(5B):2736-2749.
[16]Li Y,Jia D,Shaw J,et al.Structural interpretation of thecoseismic faults of the Wenchuan earthquake:Three-dimensional modeling of the Longmen Shan fold-and-thrustbelt.J.Geophys.Res.,2010,115(B4):doi:10.1029/2009JB006824.
[17]刘静,张智慧,文力等.汶川8级大地震同震破裂的特殊性及构造意义—多条平行断裂同时活动的反序型逆冲地震事件.地质学报,2008,82(12):1707-1722.Liu J,Zhang Z H,Wen L,et al.The Ms8.0 Wenchuanearthquake co-seismic rupture and its tectonic implications—An out-of-sequence thrusting event with slip partitioned onmultiple faults.Acta Geol.Sin.(in Chinese),2008,82(12):1707-1722.
[18]李海兵,付小方,van Der Woerd J等.汶川地震(Ms8.0)地表破裂及其同震右旋斜向逆冲作用.地质学报,2008,82(12):1623-1643.Li H B,Fu X F,van Der Woerd J,et al.Co-seisimic surfacerupture and dextral-slip oblique thrusting of the Ms8.0Wenchuan Earthquake.Acta Geol.Sin.(in Chinese),2008,82(12):1623-1643.
[19]Draper N,Smith H.Applied Regression Analysis.2nd ed.New York:Wiley,1981.
[20]张勇,冯万鹏,许力生等.2008年汶川大地震的时空破裂过程.中国科学(D辑),2008,38(10):1186-1194.Zhang Y,Feng W P,Xu L S,et al.Spatio-temporal ruptureprocess of the 2008great Wenchuan earthquake.Sci.inChina(Ser.D),2009,52(2):145-152.
[21]王卫民,赵连锋,李娟等.四川汶川8.0级地震震源过程.地球物理学报,2008,51(5):1403-1410.Wang W M,Zhao L F,Li J,et al.Rupture process of theMs8.0Wenchuan earthquake of Sichuan,China.Chinese J.Geophys.(in Chinese),2008,51(5):1403-1410.
[22]Du Y J,Aydin A,Segall P.Comparison of various inversiontechniques as applied to the determination of a geophysicaldeformation model for the 1983 Borah Peak earthquake.Bull.Seism.Soc.Am.,1992,82:1840-1866.
[23]Johnson K M,Segall P.Imaging the ramp-décollementgeometry of the Chelungpu fault using coseismic GPSdisplacements from the 1999 Chi-Chi,Taiwan earthquake.Tectonophysics,2004,378(1-2):123-139.
[24]Pathier E,Fielding E J,Wright T J,et al.Displacementfield and slip distribution of the 2005 Kashmir earthquakefrom SAR imagery.Geophys.Res.Lett.,2006,33(20):doi:10.1029/2006GL027193.
[25]朱艾斓,徐锡伟,周永胜等.川西地区小震重新定位及其活动构造意义.地球物理学报,2005,48(3):629-636.Zhu A L,Xu X W,Zhou Y S,et al.Relocation of smallearthquakes in western Sichuan,China and its implicationsfor active tectonics.Chinese J.Geophys.(in Chinese),2005,48(3):629-636.
[26]Hsu Y J,Segall P,Yu S B,et al.Temporal and spatialvariations of post-seismic deformation following the 1999Chi-Chi,Taiwan earthquake.Geophys.J.Int.,2007,169(2):367-379.
[27]Heki K,Miyazaki S,Tsuji H.Silent fault slip following aninterplate thrust earthquake at the Japan Trench.Nature,1997,386(6625):595-598.
[28]刘树根,李智武,曹俊兴等.龙门山陆内复合造山带的四维结构构造特征.地质科学,2009,44(4):1151-1180.Liu S G,Li Z W,Cao J X,et al.4-D textural and structuralcharacteristics of Longmen intracontinental orogenic belt,southwest China.Chinese Journal of Geology(in Chinese),2009,44(4):1151-1180.
[29]许志琴,侯立炜,王宗秀等.中国松潘一甘孜造山带的造山过程.北京:地质出版社,1992.Xu Z Q,Hou L W,Wang Z X,et al.Orogenic Processes ofthe Songpan Ganze Orogenic Belt of China(in Chinese).Beijing:Geological Publishing House,1992.
[30]朱介寿.汶川地震的岩石圈深部结构与动力学背景.成都理工大学学报(自然科学版),2008,35(4):348-356.Zhu J S.The Wenchuan earthquake occurrence background indeep structure and dynamics of lithosphere.Journal ofChengdu University of Technology(Science&TechnologyEdition)(in Chinese),2008,35(4):348-356.
[31]Zhang Z,Wang Y,Chen Y,et al.Crustal structure acrossLongmenshan fault belt from passive source seismic profiling.Geophys.Res.Lett.,2009,36(17):doi:10.1029/2009GL039580.
[32]Wang C,Zhu L,Lou H,et al.Crustal thicknesses andPoisson′s ratios in the eastern Tibetan Plateau and theirtectonic implications.J.Geophys.Res.,2010,115(B11):doi:10.1029/2010JB007527.
[33]Robert A,Zhu J,Vergne J,et al.Crustal structures in thearea of the 2008Sichuan earthquake from seismologic andgravimetric data.Tectonophysics,2010,491(1-4):205-210.
[34]刘启元,李昱,陈九辉等.汶川Ms8.0地震:地壳上地幔S波速度结构的初步研究.地球物理学报,2009,52(2):309-319.Liu Q Y,Li Y,Chen J H,et al.Wenchuan Ms8.0earthquake:preliminary study of the S-wave velocity structure ofthe crust and upper mantle.Chinese J.Geophys.(in Chinese),2009,52(2):309-319.
[2]Avouac J.Dynamic processes in extensional and compressionalsettings-mountain building:From earthquakes to geologicaldeformation.Treatise on Geophysics,2008,6:377-439.
[3]Shen Z K,Sun J B,Zhang P Z,et al.Slip maxima at faultjunctions and rupturing of barriers during the 2008Wenchuanearthquake.Nat.Geosci.,2009,2:718-724.
[4]闻学泽,张培震,杜方等.2008年汶川8.0级地震发生的历史与现今地震活动背景.地球物理学报,2009,52(2):444-454.Wen X Z,Zhang P Z,Du F,et al.The background ofhistorical and modern seismic activities of the occurrence ofthe 2008 Ms8.0Wenchuan,Sichuan,earthquake.Chinese J.Geophys.(in Chinese),2009,52(2):444-454.
[5]Royden L H,Burchfiel B C,King R W,et al.Surfacedeformation and lower crustal flow in eastern Tibet.Science,1997,276(5313):788-790.
[6]杨少敏,兰启贵,聂兆生等.用多种数据构建2008年汶川特大地震同震位移场.地球物理学报,2012,55(8):2575-2588.Yang S M,Lan Q G,Nie Z S,et al.Coseismic displacementcaused by the 2008great Wenchuan earthquake derived fromvarious types of geodetic data.Chinese J.Geophys.(inChinese),2012,55(8):2575-2588.
[7]孙建宝,梁芳,沈正康等.汶川Ms8.0地震InSAR形变观测及初步分析.地震地质,2008,30(3):789-795.Sun J B,Liang F,Shen Z K,et al.InSAR deformationobservation and preliminary analysis of the Ms8.0 Wenchuanearthquake.Seismology and Geology(in Chinese),2008,30(3):789-795.
[8]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.地球物理学报,2009,52(2):390-397.Chen J H,Liu Q Y,Li S C,et al.Seismotectonic study byrelocation of the Wenchuan Ms8.0 earthquake sequence.Chinese J.Geophys.(in Chinese),2009,52(2):390-397.
[9]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.地震地质,2008,30(3):597-629.Xu X W,Wen X Z,Ye J Q,et al.The Ms8.0 Wenchuanearthquake surface ruptures and its seismogenic structure.Seismology and Geology(in Chinese),2008,30(3):597-629.
[10]Wang Q,Qiao X J,Lan Q G,et al.Rupture of deep faults inthe 2008 Wenchuan earthquake and uplift of the LongmenShan.Nature Geosci.,2011,4:634-640.
[11]Okada Y.Surface deformation due to shear and tensile faultsin a half-space.Bull.Seismol.Soc.Am.,1985,75:1135-1154.
[12]王敏.基于GPS同震位移场约束反演2008年5.12汶川大地震破裂空间分布.地球物理学报,2009,52(10):2519-2526.Wang M.Coseismic slip distribution of the 2008 Wenchuangreat earthquake constrained using GPS coseismic displacementfield.Chinese J.Geophys.(in Chinese),2009,52(10):2519-2526.
[13]Feng G C,Hetland E A,Ding X L,et al.Coseismic faultslip of the 2008 Mw7.9Wenchuan earthquake estimated fromInSAR and GPS measurements.Geophys.Res.Lett.,2010,37(1):doi:10.1029/2009GL041213.
[14]Tong X P,Sandwell D T,Fialko Y R.Coseismic slip modelof the 2008Wenchuan earthquake derived from joint inversionof interferometric synthetic aperture radar,GPS,and fielddata.J.Geophys.Res.,2010,115(B4),doi:10.1029/2009JB006625.
[15]Xu C J,Liu Y,Wen Y M,et al.Coseismic slip distributionof the 2008 Mw7.9Wenchuan earthquake from joint inversionof GPS and InSAR data.Bull.Seism.Soc.Am.,2010,100(5B):2736-2749.
[16]Li Y,Jia D,Shaw J,et al.Structural interpretation of thecoseismic faults of the Wenchuan earthquake:Three-dimensional modeling of the Longmen Shan fold-and-thrustbelt.J.Geophys.Res.,2010,115(B4):doi:10.1029/2009JB006824.
[17]刘静,张智慧,文力等.汶川8级大地震同震破裂的特殊性及构造意义—多条平行断裂同时活动的反序型逆冲地震事件.地质学报,2008,82(12):1707-1722.Liu J,Zhang Z H,Wen L,et al.The Ms8.0 Wenchuanearthquake co-seismic rupture and its tectonic implications—An out-of-sequence thrusting event with slip partitioned onmultiple faults.Acta Geol.Sin.(in Chinese),2008,82(12):1707-1722.
[18]李海兵,付小方,van Der Woerd J等.汶川地震(Ms8.0)地表破裂及其同震右旋斜向逆冲作用.地质学报,2008,82(12):1623-1643.Li H B,Fu X F,van Der Woerd J,et al.Co-seisimic surfacerupture and dextral-slip oblique thrusting of the Ms8.0Wenchuan Earthquake.Acta Geol.Sin.(in Chinese),2008,82(12):1623-1643.
[19]Draper N,Smith H.Applied Regression Analysis.2nd ed.New York:Wiley,1981.
[20]张勇,冯万鹏,许力生等.2008年汶川大地震的时空破裂过程.中国科学(D辑),2008,38(10):1186-1194.Zhang Y,Feng W P,Xu L S,et al.Spatio-temporal ruptureprocess of the 2008great Wenchuan earthquake.Sci.inChina(Ser.D),2009,52(2):145-152.
[21]王卫民,赵连锋,李娟等.四川汶川8.0级地震震源过程.地球物理学报,2008,51(5):1403-1410.Wang W M,Zhao L F,Li J,et al.Rupture process of theMs8.0Wenchuan earthquake of Sichuan,China.Chinese J.Geophys.(in Chinese),2008,51(5):1403-1410.
[22]Du Y J,Aydin A,Segall P.Comparison of various inversiontechniques as applied to the determination of a geophysicaldeformation model for the 1983 Borah Peak earthquake.Bull.Seism.Soc.Am.,1992,82:1840-1866.
[23]Johnson K M,Segall P.Imaging the ramp-décollementgeometry of the Chelungpu fault using coseismic GPSdisplacements from the 1999 Chi-Chi,Taiwan earthquake.Tectonophysics,2004,378(1-2):123-139.
[24]Pathier E,Fielding E J,Wright T J,et al.Displacementfield and slip distribution of the 2005 Kashmir earthquakefrom SAR imagery.Geophys.Res.Lett.,2006,33(20):doi:10.1029/2006GL027193.
[25]朱艾斓,徐锡伟,周永胜等.川西地区小震重新定位及其活动构造意义.地球物理学报,2005,48(3):629-636.Zhu A L,Xu X W,Zhou Y S,et al.Relocation of smallearthquakes in western Sichuan,China and its implicationsfor active tectonics.Chinese J.Geophys.(in Chinese),2005,48(3):629-636.
[26]Hsu Y J,Segall P,Yu S B,et al.Temporal and spatialvariations of post-seismic deformation following the 1999Chi-Chi,Taiwan earthquake.Geophys.J.Int.,2007,169(2):367-379.
[27]Heki K,Miyazaki S,Tsuji H.Silent fault slip following aninterplate thrust earthquake at the Japan Trench.Nature,1997,386(6625):595-598.
[28]刘树根,李智武,曹俊兴等.龙门山陆内复合造山带的四维结构构造特征.地质科学,2009,44(4):1151-1180.Liu S G,Li Z W,Cao J X,et al.4-D textural and structuralcharacteristics of Longmen intracontinental orogenic belt,southwest China.Chinese Journal of Geology(in Chinese),2009,44(4):1151-1180.
[29]许志琴,侯立炜,王宗秀等.中国松潘一甘孜造山带的造山过程.北京:地质出版社,1992.Xu Z Q,Hou L W,Wang Z X,et al.Orogenic Processes ofthe Songpan Ganze Orogenic Belt of China(in Chinese).Beijing:Geological Publishing House,1992.
[30]朱介寿.汶川地震的岩石圈深部结构与动力学背景.成都理工大学学报(自然科学版),2008,35(4):348-356.Zhu J S.The Wenchuan earthquake occurrence background indeep structure and dynamics of lithosphere.Journal ofChengdu University of Technology(Science&TechnologyEdition)(in Chinese),2008,35(4):348-356.
[31]Zhang Z,Wang Y,Chen Y,et al.Crustal structure acrossLongmenshan fault belt from passive source seismic profiling.Geophys.Res.Lett.,2009,36(17):doi:10.1029/2009GL039580.
[32]Wang C,Zhu L,Lou H,et al.Crustal thicknesses andPoisson′s ratios in the eastern Tibetan Plateau and theirtectonic implications.J.Geophys.Res.,2010,115(B11):doi:10.1029/2010JB007527.
[33]Robert A,Zhu J,Vergne J,et al.Crustal structures in thearea of the 2008Sichuan earthquake from seismologic andgravimetric data.Tectonophysics,2010,491(1-4):205-210.
[34]刘启元,李昱,陈九辉等.汶川Ms8.0地震:地壳上地幔S波速度结构的初步研究.地球物理学报,2009,52(2):309-319.Liu Q Y,Li Y,Chen J H,et al.Wenchuan Ms8.0earthquake:preliminary study of the S-wave velocity structure ofthe crust and upper mantle.Chinese J.Geophys.(in Chinese),2009,52(2):309-319.
版权所有：© 2023 中国地质图书馆 中国地质调查局地学文献中心