青藏高原北部大型走滑断裂带近地表地质变形带特征分析
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摘要
阿尔金断裂带、东昆仑断裂带和海原断裂带是青藏高原北部的大型左旋走滑断裂带,具有相对高的地质和GPS滑动速率,地表破裂型地震频发。在阿尔金断裂带阿克塞老城西和半果巴、东昆仑断裂带西大滩和玛沁、海原断裂带松山等地点的探槽地质剖面揭露了这些走滑断裂带累积地质变形带的基本特征。阿尔金断裂带半果巴探槽和阿克塞老城西探槽、东昆仑断裂带西大滩探槽和玛沁探槽揭露出的地质变形带宽度约12m左右;海原断裂带松山拉分盆地边界单条走滑断层地质变形带宽度不足10m,考虑到地震期间拉分盆地可能会出现较严重的变形,则拉分盆地本身也应作为强变形带处理。由此可见,经历过多个地震地表破裂循环的东昆仑断裂带、海原断裂带和阿尔金断裂带其地质变形带的宽度是有限的,具有变形局部化特征。单条走滑断层的地质变形带宽度一般为10余米,比较保守地估计应<30m,走滑断层斜列阶区的地质变形带宽度取决于阶区本身的宽度。
The Altyn Tagh,Kunlun and Haiyuan Faults are three major left-lateral strike-slip faults with high geologic and GPS-derived horizontal slip rates as well as frequent surface-rupturing earthquakes in the northern Tibetan Plateau.There exist local structures,such as pull-apart basins in stepovers and sag ponds,where fine-grained and/or organic interfaulting sediments have been continuously filled and co-seismic faulting traces have been well preserved in those sediments.Trenching across the strike-slip faults and those local structures,stratum-logging of the trench walls and structural-stratigraphic examination can uncover basic features of the permanent and cumulative geologic deformation zone of a strike-slip fault that has experienced several surface-rupturing earthquake cycles.The geologic section of the Banguoba trench 9km east of Old A'kesai Town across the recent traces of the Altyn Tagh Fault records 7 paleoearthquake events with a co-seismic left-lateral slip of 7±1m for the latest event and its cumulative geologic deformation zone is only 8m in width.The geologic section of the western Old A'kesai trench across a pull-apart basin of the Altyn Tagh Fault records at least 4 paleoearthquake events and its permanent and cumulative geologic deformation zone is only 13m in width.The geologic section of the Xidatan trench across the Kunlun Fault reveals 5 paleoearthquake events and their cumulative geologic deformation zones are 12～13m in width.The Maqin trench across a pull-apart of the Kunlun Fault also reveals 5 paleo-earthquake events and most of the structural deformation,about 15m wide,is concentrated in the pull-apart,while the widest structural deformation,including the associated distortion nearby the boundary fault of the pull-apart,is less than 35m.Two trenches excavated across the southern and northern boundary faults of the Songshan pull-apart basin along the Maomaoshan-Laohuashan segment of the Haiyuan Fault show up 6 paleoevents and their permanent geologic deformation zones are less than 10m wide for single boundary fault.Of course,as a extensional jog,the pull-apart basin over a hundred meters wide will experience severe tensional and transtensional surface ruptures during an earthquake,and the pull-apart basin itself may be taken as one part of the permanent geologic deformation zone.Thus,the repeatedly faulting of the Altyn Tagh,Kunlun,and Haiyuan Faults during the past several surface-rupturing earthquake cycles is localized along their strike and the width of their permanent geologic deformation zone for a single strike-slip fault is over 10 meters,but less than 30 meters in general.
The Altyn Tagh,Kunlun and Haiyuan Faults are three major left-lateral strike-slip faults with high geologic and GPS-derived horizontal slip rates as well as frequent surface-rupturing earthquakes in the northern Tibetan Plateau.There exist local structures,such as pull-apart basins in stepovers and sag ponds,where fine-grained and/or organic interfaulting sediments have been continuously filled and co-seismic faulting traces have been well preserved in those sediments.Trenching across the strike-slip faults and those local structures,stratum-logging of the trench walls and structural-stratigraphic examination can uncover basic features of the permanent and cumulative geologic deformation zone of a strike-slip fault that has experienced several surface-rupturing earthquake cycles.The geologic section of the Banguoba trench 9km east of Old A'kesai Town across the recent traces of the Altyn Tagh Fault records 7 paleoearthquake events with a co-seismic left-lateral slip of 7±1m for the latest event and its cumulative geologic deformation zone is only 8m in width.The geologic section of the western Old A'kesai trench across a pull-apart basin of the Altyn Tagh Fault records at least 4 paleoearthquake events and its permanent and cumulative geologic deformation zone is only 13m in width.The geologic section of the Xidatan trench across the Kunlun Fault reveals 5 paleoearthquake events and their cumulative geologic deformation zones are 12～13m in width.The Maqin trench across a pull-apart of the Kunlun Fault also reveals 5 paleo-earthquake events and most of the structural deformation,about 15m wide,is concentrated in the pull-apart,while the widest structural deformation,including the associated distortion nearby the boundary fault of the pull-apart,is less than 35m.Two trenches excavated across the southern and northern boundary faults of the Songshan pull-apart basin along the Maomaoshan-Laohuashan segment of the Haiyuan Fault show up 6 paleoevents and their permanent geologic deformation zones are less than 10m wide for single boundary fault.Of course,as a extensional jog,the pull-apart basin over a hundred meters wide will experience severe tensional and transtensional surface ruptures during an earthquake,and the pull-apart basin itself may be taken as one part of the permanent geologic deformation zone.Thus,the repeatedly faulting of the Altyn Tagh,Kunlun,and Haiyuan Faults during the past several surface-rupturing earthquake cycles is localized along their strike and the width of their permanent geologic deformation zone for a single strike-slip fault is over 10 meters,but less than 30 meters in general.
引文
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冉勇康,段瑞涛,邓起东,等.1997.海原断裂高弯子地点三维探槽的开挖与古地震研究[J].地震地质,19(2):97—107.RAN Yong-kang,DUANRui-tao,DENG Qi-dong,et al.1997.3-D trench excavation and Paleoseismology at Gaowan-zi on the Haiyuan Fault[J].Seismology and Geology,19(2):97—107(in Chinese).
徐锡伟,于贵华,马文涛,等.2002a.活断层地震地表破裂“避让带”宽度确定依据与方法[J].地震地质,24(4):469—483.XU Xi-wei,YU Gui-hua,MA Wen-tao,et al.2002a.Evidence and methods for determining the safety distance fromthe potential earthquake surface rupture on active fault[J].Seismology and Geology,24(4):469—483(in Chi-nese).
徐锡伟,陈文彬,于贵华,等.2002b.2001年11月14日昆仑山库赛湖地震(MS8.1)地表破裂带基本特征[J].地震地质,24(1):1—13.XU Xi-wei,CHEN Wen-bin,YU Gui-hua,et al.2002b.Characteristic features of the surface ruptures of the HOHSAI HU(KUNLUNSHAN)earthquake(MS8.1),northern Tibetan Plateau,China[J].Seismology and Geolo-gy,24(1):1—13(in Chinese).
徐锡伟,P Tapponnier,Van Der Woerd J,等.2003.阿尔金断裂带晚第四纪左旋走滑速率及其构造运动转换模型讨论[J].中国科学(D辑),33(10):967—974.XUXi-wei,Tapponnier P,Van Der Woerd J,et al.2003.Late Quaternary sinistral slip rate along the Altyn Tagh faultand its structural transformation model[J].Science in China(Ser D),48(3):384—397.
张培震,邓起东,张国民,等.2003.中国大陆强震活动与活动块体[J].中国科学(D辑),33(增刊),12—20.ZHANG Pei-zhen,DENG Qi-dong,ZHANG Guo-min,et al.2003.Active tectonic blocks and strong earthquakes inthe continent of China[J].Science in China(Ser D),46(suppl):13—24.
Deng QD,Chen S F,Song F M,et al.1986.Variation in the geometry and amount of slip on the Haiyuan(Nanxihuas-han)fault zone,China,and the surface rupture of the1920Haiyuan earthquake[A].In:Das S,et al(eds).Earthquake Source Mechanics,Geophy Monogr Ser.37,169—182,AGU,Washington,D C.
Deng Q D,Zhang P Z,Ran Y K.2003.Basic characteristics of active tectonics of China[J].Science in China(SerD),46:356—372.
Fumal TE,Weldon R J,Biasi G P,et al.2002.Evidence for large earthquakes on the San Andreas fault at theWrightwood,California paleoseismic site:A D.500to present[J].Bull Seism Soc Am,92:2726—2760.
Gaudemer Y,Tapponnier P,Meyer B,et al.1995.Partitioning of crustal slip between linked active faults in the east-ern Qilian Shan,and evidence for a major seismic gap,the Tianzhu gap,on the western Haiyuan fault,Gansu(China)[J].Geophy J,120(3):599—645.
Lasserre C,Morel P H,Gaudemer Y,et al.1999.Postglacial left slip-rate and past occurrence ofM≥8earthquakeson the western Haiyuan fault,Gansu,China[J].J Geophys Res,104:17633—17651.
Lasserre C,Bukchin B,Bernard P,et al.2002.Fast late Pleistocene slip rate on the Lenglong Ling segment of theHaiyuan Fault,Qinghai,China[J].J Geophy Res,107,B11,2276,doi10.1029/2000JB000060.
Liu-Zeng Jing,Yann Klinger,Xiwei XU,et al.2007.Millennial recurrence of large earthquakes on the Haiyuan faultnear Songshan,Gansu Province,China[J].Bulletin of Seismological Society of America,97(18):14—34,doi:10.1785/0120050118.
Meriaux A S,Ryerson F J,Tapponnier P,et al.2004.Rapid slip along the central Altyn Tagh fault:morphochrono-logic evidence from Cherchen He and Sulamu Tagh[J].J Geophy Res,109,B06401,doi06410.01029/02003JB002558.
Peltzer G,Cramp F,King J,et al.1999.Evidence of nonlinear elasticity of the crust fromMW7.6Manyi(Tibet)earthquake[J].Science,286:273—276.
Shen F,Leigh HR,Burchfiel B C.2001.Large-scale crustal deformation of the Tibetan Plateau[J].J Geophy Res,106(B4):6793—6816.
Sieh K.1978.Prehistoric large earthquakes produced by slip on the San Andreas fault at Pallett Creek,California[J].J Geophy Res,83:3907—3939.
Van Der Woerd J,Ryerson F J,Tapponnier P,et al.1998.Holocene left slip-rate determined by cosmogenic surfacedating on the Xidatan segment of the Kunlun fault(Qinghai,China)[J].Geology,26:695—698.
Van Der Woerd J,Ryerson F J,Tapponnier P,et al.2000.Uniform slip-rate along the Kunlun fault:Implication forseismic behaviour and large-scale tectonics[J].Geophys Res Lett,27:2353—2356.
Wallace K,Yin G,Bilham R.2005.Inescapable low slip on the Altyn Tagh fault[J].Geophy Res Lett,31,L09613,doi10.1029/2004GL019724.
Weldon R,McCalpin and Rockwell TK.1996.Paleoseismology of strike-slip tectonic environments[A].In:McCap-in J(ed).Paleoseismology.Academic Press,San Diego.271—329.
XU Xiwei,YU Guihua,Klinger Y,et al.2006.Re-evaluation of surface rupture parameters and faulting segmentationof the2001Kunlunshan earthquake(MW7.8),Northern Tibetan Plateau,China[J].Journal of GeophysicalResearch,111,B05316,doi:10.1029/2004JB003488.
Xu X W,Chen W B,Ma W T,et al.2002.Surface rupture of the Kunlun earthquake(MS8.1),Northern TibetanPlateau,China[J].Seismological Research Letters,73(6):884—892.
Yeats R S,Sieh K,Allen C R.1997.The Geology of Earthquakes[M].Oxford Univ Press,Oxford.568.
Zhang P,Molnar P,Burchfile B C,et al.1988,Bounds on the Holocene slip rate of the Haiyuan fault,north centralChina[J].Quat Res,30:151—164.
Zheng-Kang Shen,Min Wang,Yanxing Li,et al.2001.Crustal deformation along the Altyn Tagh fault system,westernChina,from GPS[J].Journal of Geophysical Research,106(B12):30607—30622.
Zhang P,Shen Z,Wang M,et al.2004.Continuous deformation of the Tibetan Plateau from Global Positioning Sys-tem data[J].Geology,32:809—812.
青海省地震局,中国地震局地壳应力研究所.1999.东昆仑活动断裂带[M].北京:地震出版社.186.Qinghai Earthquake Administration&Institute of Geodynamics,CEA.1999.Eastern Kunlun Active Fault Zone[M].Seismological Press,Beijing.186(in Chinese).
冉勇康,段瑞涛,邓起东,等.1997.海原断裂高弯子地点三维探槽的开挖与古地震研究[J].地震地质,19(2):97—107.RAN Yong-kang,DUANRui-tao,DENG Qi-dong,et al.1997.3-D trench excavation and Paleoseismology at Gaowan-zi on the Haiyuan Fault[J].Seismology and Geology,19(2):97—107(in Chinese).
徐锡伟,于贵华,马文涛,等.2002a.活断层地震地表破裂“避让带”宽度确定依据与方法[J].地震地质,24(4):469—483.XU Xi-wei,YU Gui-hua,MA Wen-tao,et al.2002a.Evidence and methods for determining the safety distance fromthe potential earthquake surface rupture on active fault[J].Seismology and Geology,24(4):469—483(in Chi-nese).
徐锡伟,陈文彬,于贵华,等.2002b.2001年11月14日昆仑山库赛湖地震(MS8.1)地表破裂带基本特征[J].地震地质,24(1):1—13.XU Xi-wei,CHEN Wen-bin,YU Gui-hua,et al.2002b.Characteristic features of the surface ruptures of the HOHSAI HU(KUNLUNSHAN)earthquake(MS8.1),northern Tibetan Plateau,China[J].Seismology and Geolo-gy,24(1):1—13(in Chinese).
徐锡伟,P Tapponnier,Van Der Woerd J,等.2003.阿尔金断裂带晚第四纪左旋走滑速率及其构造运动转换模型讨论[J].中国科学(D辑),33(10):967—974.XUXi-wei,Tapponnier P,Van Der Woerd J,et al.2003.Late Quaternary sinistral slip rate along the Altyn Tagh faultand its structural transformation model[J].Science in China(Ser D),48(3):384—397.
张培震,邓起东,张国民,等.2003.中国大陆强震活动与活动块体[J].中国科学(D辑),33(增刊),12—20.ZHANG Pei-zhen,DENG Qi-dong,ZHANG Guo-min,et al.2003.Active tectonic blocks and strong earthquakes inthe continent of China[J].Science in China(Ser D),46(suppl):13—24.
Deng QD,Chen S F,Song F M,et al.1986.Variation in the geometry and amount of slip on the Haiyuan(Nanxihuas-han)fault zone,China,and the surface rupture of the1920Haiyuan earthquake[A].In:Das S,et al(eds).Earthquake Source Mechanics,Geophy Monogr Ser.37,169—182,AGU,Washington,D C.
Deng Q D,Zhang P Z,Ran Y K.2003.Basic characteristics of active tectonics of China[J].Science in China(SerD),46:356—372.
Fumal TE,Weldon R J,Biasi G P,et al.2002.Evidence for large earthquakes on the San Andreas fault at theWrightwood,California paleoseismic site:A D.500to present[J].Bull Seism Soc Am,92:2726—2760.
Gaudemer Y,Tapponnier P,Meyer B,et al.1995.Partitioning of crustal slip between linked active faults in the east-ern Qilian Shan,and evidence for a major seismic gap,the Tianzhu gap,on the western Haiyuan fault,Gansu(China)[J].Geophy J,120(3):599—645.
Lasserre C,Morel P H,Gaudemer Y,et al.1999.Postglacial left slip-rate and past occurrence ofM≥8earthquakeson the western Haiyuan fault,Gansu,China[J].J Geophys Res,104:17633—17651.
Lasserre C,Bukchin B,Bernard P,et al.2002.Fast late Pleistocene slip rate on the Lenglong Ling segment of theHaiyuan Fault,Qinghai,China[J].J Geophy Res,107,B11,2276,doi10.1029/2000JB000060.
Liu-Zeng Jing,Yann Klinger,Xiwei XU,et al.2007.Millennial recurrence of large earthquakes on the Haiyuan faultnear Songshan,Gansu Province,China[J].Bulletin of Seismological Society of America,97(18):14—34,doi:10.1785/0120050118.
Meriaux A S,Ryerson F J,Tapponnier P,et al.2004.Rapid slip along the central Altyn Tagh fault:morphochrono-logic evidence from Cherchen He and Sulamu Tagh[J].J Geophy Res,109,B06401,doi06410.01029/02003JB002558.
Peltzer G,Cramp F,King J,et al.1999.Evidence of nonlinear elasticity of the crust fromMW7.6Manyi(Tibet)earthquake[J].Science,286:273—276.
Shen F,Leigh HR,Burchfiel B C.2001.Large-scale crustal deformation of the Tibetan Plateau[J].J Geophy Res,106(B4):6793—6816.
Sieh K.1978.Prehistoric large earthquakes produced by slip on the San Andreas fault at Pallett Creek,California[J].J Geophy Res,83:3907—3939.
Van Der Woerd J,Ryerson F J,Tapponnier P,et al.1998.Holocene left slip-rate determined by cosmogenic surfacedating on the Xidatan segment of the Kunlun fault(Qinghai,China)[J].Geology,26:695—698.
Van Der Woerd J,Ryerson F J,Tapponnier P,et al.2000.Uniform slip-rate along the Kunlun fault:Implication forseismic behaviour and large-scale tectonics[J].Geophys Res Lett,27:2353—2356.
Wallace K,Yin G,Bilham R.2005.Inescapable low slip on the Altyn Tagh fault[J].Geophy Res Lett,31,L09613,doi10.1029/2004GL019724.
Weldon R,McCalpin and Rockwell TK.1996.Paleoseismology of strike-slip tectonic environments[A].In:McCap-in J(ed).Paleoseismology.Academic Press,San Diego.271—329.
XU Xiwei,YU Guihua,Klinger Y,et al.2006.Re-evaluation of surface rupture parameters and faulting segmentationof the2001Kunlunshan earthquake(MW7.8),Northern Tibetan Plateau,China[J].Journal of GeophysicalResearch,111,B05316,doi:10.1029/2004JB003488.
Xu X W,Chen W B,Ma W T,et al.2002.Surface rupture of the Kunlun earthquake(MS8.1),Northern TibetanPlateau,China[J].Seismological Research Letters,73(6):884—892.
Yeats R S,Sieh K,Allen C R.1997.The Geology of Earthquakes[M].Oxford Univ Press,Oxford.568.
Zhang P,Molnar P,Burchfile B C,et al.1988,Bounds on the Holocene slip rate of the Haiyuan fault,north centralChina[J].Quat Res,30:151—164.
Zheng-Kang Shen,Min Wang,Yanxing Li,et al.2001.Crustal deformation along the Altyn Tagh fault system,westernChina,from GPS[J].Journal of Geophysical Research,106(B12):30607—30622.
Zhang P,Shen Z,Wang M,et al.2004.Continuous deformation of the Tibetan Plateau from Global Positioning Sys-tem data[J].Geology,32:809—812.
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