龙门山山前疑似汶川M_S 8.0地震地表破裂的浅层地震反射调查
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摘要
2008年5月12日发生在龙门山构造带的汶川MS8.0大地震是映秀-北川断裂突发错动的结果。此次地震不但使NE向的映秀-北川断裂和灌县-江油断裂发生了地表破裂,而且,在成都平原区的什邡、绵竹等地也出现了不同程度的地表裂缝、公路拱曲以及带状的喷砂冒水现象。此项探测研究以出现在什邡市师古镇附近的疑似地震地表破裂带为切入点,通过采用可控震源以及高精度的浅层地震反射勘探方法,获得了深度15～800m范围内高分辨率的地下结构和构造图像。结果表明,在地表破裂之下存在向平原区逆冲的隐伏断层和反向的逆冲断层,地震过程中隐伏逆断层的活动可能是近地表地层出现褶皱变形和地表破裂的主要原因。
The MS 8.0 great Wenchuan earthquake of May 12th,2008 was generated by abrupt faulting of the Yingxiu-Beichuan Fault along the Longmenshan Fault zone.The earthquake produced not only the surface ruptures along the Yingxiu-Beichuan Fault and Guanxian-Jiangyou Fault,but also surface rupture,highway's pavement arching,sand-boils and waterspouts in various degrees in the areas such as Shifang and Mianzhu of the Chengdu plain.To know the shallow geological structures under the surface rupture zone,a high-resolution shallow seismic reflection profile of 6350m long in near-EW direction was completed.This profile is located at the Shigu town,Shifang city,where a suspected earthquake surface rupture zone was discovered.In this study,a trace interval of 3m,shot interval of 18m,and a 300-channel 25-fold observation system was used.In order to give consideration of both near-surface reflections and dipping interface imaging,we adopted the split-spread geometry and asymmetrical zero-offset receiving technique.For suppressing random-noise and raising signal to noise ratio of seismic data,30 times vertical stacking of vibrator signals was made for each common-shot gather after correlation of individual records.By using the above work method and spread geometry,we obtained high-resolution images of structures in the depth range of 15～800m after data processing.The result shows that there are the buried thrust fault thrusting to the plain and the back-thrust fault under surface rupture zone,and that the activity of the buried thrust fault may be the main causes for folding and deformation in near-surface strata and for the coseismic surface rupturing.
The MS 8.0 great Wenchuan earthquake of May 12th,2008 was generated by abrupt faulting of the Yingxiu-Beichuan Fault along the Longmenshan Fault zone.The earthquake produced not only the surface ruptures along the Yingxiu-Beichuan Fault and Guanxian-Jiangyou Fault,but also surface rupture,highway's pavement arching,sand-boils and waterspouts in various degrees in the areas such as Shifang and Mianzhu of the Chengdu plain.To know the shallow geological structures under the surface rupture zone,a high-resolution shallow seismic reflection profile of 6350m long in near-EW direction was completed.This profile is located at the Shigu town,Shifang city,where a suspected earthquake surface rupture zone was discovered.In this study,a trace interval of 3m,shot interval of 18m,and a 300-channel 25-fold observation system was used.In order to give consideration of both near-surface reflections and dipping interface imaging,we adopted the split-spread geometry and asymmetrical zero-offset receiving technique.For suppressing random-noise and raising signal to noise ratio of seismic data,30 times vertical stacking of vibrator signals was made for each common-shot gather after correlation of individual records.By using the above work method and spread geometry,we obtained high-resolution images of structures in the depth range of 15～800m after data processing.The result shows that there are the buried thrust fault thrusting to the plain and the back-thrust fault under surface rupture zone,and that the activity of the buried thrust fault may be the main causes for folding and deformation in near-surface strata and for the coseismic surface rupturing.
引文
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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[J].沉积学报,24(2):153—163.LI Yong,ZHOURong-jun,Densmore A L,et al.2006.Sedimentary responses to late Cenozoic thrusting and strike-slip-ping of Longmen Shan along eastern margin of Tibetan Plateau[J].Acta Sedimentologica Sinica,24(2):153—163(in Chinese).
李永昭,郭兵.2008.成都平原的晚新生代构造[J].成都理工大学学报(自然科学版),35(4):371—376.LI Yong-zhao,GUO bing.2008.Cenozonic tectonics of Chengdu plain,Sichuan,China[J].Journal of Chengdu Univer-sity of Technology(Science&Technology Edition),35(4):371—376(in Chinese).
刘保金,张先康,方盛明,等.2002.城市活断层探测的高分辨率浅层地震数据采集技术[J].地震地质,24(4):524—532.LIU Bao-jin,ZHANG Xian-kang,FANG Sheng-ming,et al.2002.High-resolution shallow seismic data acquisition tech-nique for surveying of urban active faults[J].Seismology and Geology,24(4):524—531(in Chinese).
刘保金,柴炽章,酆少英,等.2008.第四纪沉积区断层及其上断点探测的地震方法技术:以银川隐伏活动断层为例[J].地球物理学报,51(5):1475—1483.LIU Bao-jin,CHAI Chi-zhang,FENG Shao-ying,et al.2008.Seismic exploration method for buried fault and its upperbreak point survey in Quaternary sediment area:An example of Yinchuan buried active fault[J].Chinese J Geo-phys,51(5):1475—1483(in Chinese).
唐荣昌,韩渭宾主编.1993.四川活动断裂与地震[M].北京:地震出版社.123—132.TANG Rong-chang,HAN Wei-bin(eds).1993.Active Faults and Earthquakes in Sichuan Province[M].Seismologi-cal Press,Beijing.123—132(in Chinese).
王卫民,赵连锋,李娟,等.2008.四川汶川8.0级地震震源过程[J].地球物理学报,51(5):1403—1410.WANG Wei-min,ZHAO Lian-feng,LI Juan,et al.2008.Rupture process of theMS8.0Wenchuan earthquake of Si-chuan,China[J].Chinese J Geophys,51(5):1403—1410(in Chinese).
徐锡伟,张培震,闻学泽,等.2005.川西及其邻近地区活动构造基本特征与强震复发模型[J].地震地质,27(3):446—460.XU Xi-wei,ZHANG Pei-zhen,WEN Xue-ze,et al.2005.Features of active tectonics and recurrence behaviors of strongearthquake in the western Sichuan Province and its adjacent regions[J].Seismology and Geology,27(3):446—460(in Chinese).
徐锡伟,闻学泽,叶建青,等.2008.汶川MS8.0地震地表破裂带及其发震构造[J].地震地质,30(3):597—629.XU Xi-wei,WEN Xue-ze,YE Jian-qing,et al.2008.TheMS8.0Wenchuan earthquake surface ruptures and its seis-mogenic structure[J].Seismology and Geology,30(3):597—629(in Chinese).
许志琴,李化启,侯立玮,等.2007.青藏高原东缘龙门山-锦屏造山带的崛起:大型拆离断层和挤出机制[J].地质通报,26(10):1262—1276.XU Zhi-qin,LI Hua-qi,HOU Li-wei,et al.2007.Uplifting of Longmen Shan and Jinping Shan,eastern margin of theTibetan Plateau:Large scale detachment faults and their extrusion mechanism[J].Geological Bull of China,26(10):1262—1276(in Chinese).
杨晓平,蒋溥,宋方敏,等.1999.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,21(4):341—345.YANG Xiao-ping,JIANG Pu,SONG Fang-min,et al.1999.The evidence of the south Longmenshan Fault zone cuttinglate Quaternary stratum[J].Seismology and Geology,21(4):341—345(in Chinese).
张培震,徐锡伟,闻学泽,等.2008.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因[J].地球物理学报,51(4):1066—1073.ZHANG Pen-zhen,XU Xi-wei,WEN Xue-ze,et al.2008.Slip rates and recurrence interval of the Longmenshan activefault zone,and tectonic implication for the mechanism of the May12Wenchuan earthquake,2008,Sichuan,China[J].Chinese J Geophys,51(4):1066—1073(in Chinese).
周荣军,李勇,Alexander L,等.2006.青藏高原东缘活动构造[J].矿物岩石,26(2):40—51.ZHOURong-jun,LI Yong,Alexander L,et al.2006.Active tectonics of the eastern margin of the Tibetan Plateau[J].J Mineral Petrol,26(2):40—51(in Chinese).
中国地震局.2005.中国地震活动断层探测技术系统技术规程[M].北京:地震出版社.3—42.China Seismological Bureau.2005.Stipulation on technical system for China earthquake active fault surveying[M].Seismological Press,Beijing.3—42(in Chinese).
Bachrach R,Nur A.1998.High-resolution shallowseismic experiments in sand,PartⅡ:Velocities in shallowuncon-solidated sand[J].Geophysics,63(4):1234—1240.
Burchfiel B C,Royden L H,VanDer Hilst R D,et al.1995.Tectonics of the Longmen Shan and the adjacent regions,central China[J].Int Geol Rev,37(8):661—735.
Miller R D,Xia J.1998.Large near-surface velocity gradients on shallowseismic reflection data[J].Geophysics,63(4):1348—1356.
Robert B H,Cyntyia L P,Jeffrey E C.2000.Shallowseismic reflection profiling over Brevard zone,south Caroline[J].Geophysics,65(5):1388—1401.
Shen Z K,Lu J N,Wang M,et al.2005.Contemporary crustal deformation around the southeast borderland of the Tibet-an plateau[J].J Geophys Res,110:1—17.
陈国光,计凤桔,周荣军,等.2007.龙门山断裂带晚第四纪活动性分段的初步研究[J].地震地质,29(3):657—673.CHEN Guo-guang,JI Feng-ju ZHOU Rong-jun,et al.2007.Primary research of activity segmentation of LongmenshanFault zone since late-Quaternary[J].Seismology and Geology,29(3):657—673(in Chinese).
邓起东,陈社发,赵小麟,等.1994.龙门山及其邻区的构造和地震活动及动力学[J].地震地质,16(4):389—402.DENG Qi-dong,CHEN She-fa,ZHAO Xiao-lin,et al.1994.Tectonics,seismicity and dynamics of LongmenshanMountains and its adjacent regions[J].Seismology and Geology,16(4):389—402(in Chinese).
邓起东,卢造勋,杨主恩.2007.城市活动断层探测和断层活动性评价问题[J].地震地质,29(2):189—199.DENG Qi-dong,LU Zao-xun,YANG Zhu-en.2007.Remarks on urban active faults exploration and associated activityassessment[J].Seismology and Geology,29(2):189—199(in Chinese).
何鲤,刘莉萍,罗潇,等.2007.川西龙门山推覆构造特征及有利油气勘探区块预测[J].石油实验地质,29(3):247—252(in Chinese).HHLi,LIU Li-ping,LUO Xiao,et al.2007.Nappe structure characteristics and exploration potential forecast in Long-men Shan,the west of Sichuan Province[J].Petroleum Geology&Experiment,29(3):247—252(in Chinese).
何政勤,陈宇坤,叶太兰,等.2007.浅层地震勘探在沿海地区隐伏断层探测中的应用[J].地震地质,29(2):363—371.HE Zheng-qin,CHEN Yu-kun,YE Tai-lan,et al.2007.Application of shallowseismic exploration to detection of bur-ied fault in coastal areas[J].Seismology and Geological,29(2):363—371(in Chinese).
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[J].沉积学报,24(2):153—163.LI Yong,ZHOURong-jun,Densmore A L,et al.2006.Sedimentary responses to late Cenozoic thrusting and strike-slip-ping of Longmen Shan along eastern margin of Tibetan Plateau[J].Acta Sedimentologica Sinica,24(2):153—163(in Chinese).
李永昭,郭兵.2008.成都平原的晚新生代构造[J].成都理工大学学报(自然科学版),35(4):371—376.LI Yong-zhao,GUO bing.2008.Cenozonic tectonics of Chengdu plain,Sichuan,China[J].Journal of Chengdu Univer-sity of Technology(Science&Technology Edition),35(4):371—376(in Chinese).
刘保金,张先康,方盛明,等.2002.城市活断层探测的高分辨率浅层地震数据采集技术[J].地震地质,24(4):524—532.LIU Bao-jin,ZHANG Xian-kang,FANG Sheng-ming,et al.2002.High-resolution shallow seismic data acquisition tech-nique for surveying of urban active faults[J].Seismology and Geology,24(4):524—531(in Chinese).
刘保金,柴炽章,酆少英,等.2008.第四纪沉积区断层及其上断点探测的地震方法技术:以银川隐伏活动断层为例[J].地球物理学报,51(5):1475—1483.LIU Bao-jin,CHAI Chi-zhang,FENG Shao-ying,et al.2008.Seismic exploration method for buried fault and its upperbreak point survey in Quaternary sediment area:An example of Yinchuan buried active fault[J].Chinese J Geo-phys,51(5):1475—1483(in Chinese).
唐荣昌,韩渭宾主编.1993.四川活动断裂与地震[M].北京:地震出版社.123—132.TANG Rong-chang,HAN Wei-bin(eds).1993.Active Faults and Earthquakes in Sichuan Province[M].Seismologi-cal Press,Beijing.123—132(in Chinese).
王卫民,赵连锋,李娟,等.2008.四川汶川8.0级地震震源过程[J].地球物理学报,51(5):1403—1410.WANG Wei-min,ZHAO Lian-feng,LI Juan,et al.2008.Rupture process of theMS8.0Wenchuan earthquake of Si-chuan,China[J].Chinese J Geophys,51(5):1403—1410(in Chinese).
徐锡伟,张培震,闻学泽,等.2005.川西及其邻近地区活动构造基本特征与强震复发模型[J].地震地质,27(3):446—460.XU Xi-wei,ZHANG Pei-zhen,WEN Xue-ze,et al.2005.Features of active tectonics and recurrence behaviors of strongearthquake in the western Sichuan Province and its adjacent regions[J].Seismology and Geology,27(3):446—460(in Chinese).
徐锡伟,闻学泽,叶建青,等.2008.汶川MS8.0地震地表破裂带及其发震构造[J].地震地质,30(3):597—629.XU Xi-wei,WEN Xue-ze,YE Jian-qing,et al.2008.TheMS8.0Wenchuan earthquake surface ruptures and its seis-mogenic structure[J].Seismology and Geology,30(3):597—629(in Chinese).
许志琴,李化启,侯立玮,等.2007.青藏高原东缘龙门山-锦屏造山带的崛起:大型拆离断层和挤出机制[J].地质通报,26(10):1262—1276.XU Zhi-qin,LI Hua-qi,HOU Li-wei,et al.2007.Uplifting of Longmen Shan and Jinping Shan,eastern margin of theTibetan Plateau:Large scale detachment faults and their extrusion mechanism[J].Geological Bull of China,26(10):1262—1276(in Chinese).
杨晓平,蒋溥,宋方敏,等.1999.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,21(4):341—345.YANG Xiao-ping,JIANG Pu,SONG Fang-min,et al.1999.The evidence of the south Longmenshan Fault zone cuttinglate Quaternary stratum[J].Seismology and Geology,21(4):341—345(in Chinese).
张培震,徐锡伟,闻学泽,等.2008.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因[J].地球物理学报,51(4):1066—1073.ZHANG Pen-zhen,XU Xi-wei,WEN Xue-ze,et al.2008.Slip rates and recurrence interval of the Longmenshan activefault zone,and tectonic implication for the mechanism of the May12Wenchuan earthquake,2008,Sichuan,China[J].Chinese J Geophys,51(4):1066—1073(in Chinese).
周荣军,李勇,Alexander L,等.2006.青藏高原东缘活动构造[J].矿物岩石,26(2):40—51.ZHOURong-jun,LI Yong,Alexander L,et al.2006.Active tectonics of the eastern margin of the Tibetan Plateau[J].J Mineral Petrol,26(2):40—51(in Chinese).
中国地震局.2005.中国地震活动断层探测技术系统技术规程[M].北京:地震出版社.3—42.China Seismological Bureau.2005.Stipulation on technical system for China earthquake active fault surveying[M].Seismological Press,Beijing.3—42(in Chinese).
Bachrach R,Nur A.1998.High-resolution shallowseismic experiments in sand,PartⅡ:Velocities in shallowuncon-solidated sand[J].Geophysics,63(4):1234—1240.
Burchfiel B C,Royden L H,VanDer Hilst R D,et al.1995.Tectonics of the Longmen Shan and the adjacent regions,central China[J].Int Geol Rev,37(8):661—735.
Miller R D,Xia J.1998.Large near-surface velocity gradients on shallowseismic reflection data[J].Geophysics,63(4):1348—1356.
Robert B H,Cyntyia L P,Jeffrey E C.2000.Shallowseismic reflection profiling over Brevard zone,south Caroline[J].Geophysics,65(5):1388—1401.
Shen Z K,Lu J N,Wang M,et al.2005.Contemporary crustal deformation around the southeast borderland of the Tibet-an plateau[J].J Geophys Res,110:1—17.
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