汶川M_S8.0地震发震断裂大地震原地重复现象初析
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摘要
在历史记录中,成都和龙门山地区没有发生过类似汶川MS8.0地震强度的地震。那么,在地质记录中是否会存在类似震级的古地震遗迹?作者分别在中央和前山断裂中段的地表破裂带上4个地点开挖了探槽4个和剖面1个,并进行了断错地貌面的实测。文中从几个地点新老地貌面累计变形量、探槽揭露的古地震遗迹等方面讨论汶川地震发震断裂大地震原地重复现象存在的基本事实。结果表明:无论在中央断裂的小鱼洞、擂鼓镇还是前山断裂的白鹿镇、汉旺等地,汶川5.12地震之后Ⅱ级阶地断层陡坎与Ⅰ级阶地陡坎高度基本呈倍数关系,探槽揭露Ⅱ级阶地标志地层(黄砂土层)在断裂两盘的位差也是5.12地震的约2倍,显示在龙门山地区区域Ⅱ级阶地形成之后,汶川5.12地震发生之前,存在一次与汶川MS8.0地震地表变形规模相当的地震事件。
In the historical rocords,there have been no comparable earthquakes with the May 12 Wenchuan earthquake in Chengdu and Longmenshan mountain region.Then,whether the ancient earthquake traces with comparable magnitude in the geological records can be found has become an important scientific issue.The authors and other members of Wenchuan earthquake geological investigation team did fieldwork in the earthquake region for more than one month.Four trenches and one geologic section were excavated along the middle segment of surface faulting of both the central fault and the mountain front fault.And geomorphologic surfaces of deformation were measured.In this paper,we discuss the fact that there is prehistory large earthquake along the seismogenic fault of Wenchuan earthquake from analyzing the accumulated deformation of old and young fault scarps or geomorphologic surfaces,trenching,and comparing the activities of related faults and so on.The result shows that whether at Xiaoyudong,Leigu located on the central fault or Bailu,Hanwang on the mountain front fault,or at other places along the surface faulting of the the Wenchuan earthquake,the height of the fault scarp on the second terrace has a multiple relation with that on the first terrace after the Wenchuan earthquake.The 4 trenches reveal that the dislocation of the marker strata of the second terrace on both sides of fault is twice of that of the Wenchuan earthquake,which shows that there was an earthquake event with the same scale of surface deformation of this MS8.0 Wenchuan earthquake between the formation time of the second terrace in Lomhmenshan area and the May 12 Wenhucan earthquake.Key wrods:MS8.0 Wenchuan Earthquake,Longmenshan Mountains,paleoearthquake,earthquake recurrence
In the historical rocords,there have been no comparable earthquakes with the May 12 Wenchuan earthquake in Chengdu and Longmenshan mountain region.Then,whether the ancient earthquake traces with comparable magnitude in the geological records can be found has become an important scientific issue.The authors and other members of Wenchuan earthquake geological investigation team did fieldwork in the earthquake region for more than one month.Four trenches and one geologic section were excavated along the middle segment of surface faulting of both the central fault and the mountain front fault.And geomorphologic surfaces of deformation were measured.In this paper,we discuss the fact that there is prehistory large earthquake along the seismogenic fault of Wenchuan earthquake from analyzing the accumulated deformation of old and young fault scarps or geomorphologic surfaces,trenching,and comparing the activities of related faults and so on.The result shows that whether at Xiaoyudong,Leigu located on the central fault or Bailu,Hanwang on the mountain front fault,or at other places along the surface faulting of the the Wenchuan earthquake,the height of the fault scarp on the second terrace has a multiple relation with that on the first terrace after the Wenchuan earthquake.The 4 trenches reveal that the dislocation of the marker strata of the second terrace on both sides of fault is twice of that of the Wenchuan earthquake,which shows that there was an earthquake event with the same scale of surface deformation of this MS8.0 Wenchuan earthquake between the formation time of the second terrace in Lomhmenshan area and the May 12 Wenhucan earthquake.Key wrods:MS8.0 Wenchuan Earthquake,Longmenshan Mountains,paleoearthquake,earthquake recurrence
引文
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-Quarternary[J].Seismology and Geology,29(3):657-673(in Chinese).
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陈社发,邓起东,赵小麟,等.1994.龙门山中段推覆构造带及相关构造的演化历史和变形机制[J].地震地质,16(4):404-421.CHEN She-fa,DENG Qi-dong,ZHAO Xiao-lin,et al.1994.Evolutionary history and deformation mechanism of centralLongmenshan thrust-nappes and related tectonics[J].Seismology and Geology,16(4):404-421(in Chinese).
邓起东,陈社发,赵小麟.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):389-403.DENG Qi-dong,CHEN She-fa,ZHAO Xiao-lin.1994.Tectonics,scismisity and dynamics of Longmenshan Mountainsand its adjacent regions[J].Seismology and Geology,16(4):389-403(in Chinese).
何宏林,孙昭民,王世元,等.2008.汶川MS8·0地震地表破裂[J].地震地质,30(2):359-362.HE Hong-lin,SUN Zhao-min,WANG Shi-yuan,et al.2008.Rupture of theMS8·0Wenchuan earthquake[J].Seis-mology and Geology,30(2):359-362(in Chinese).
贾秋鹏,贾东,朱艾斓,等.2007.青藏高原东缘龙门山冲断带与四川盆地的现今构造表现:数字地形和地震活动证据[J].地质科学,42(1):31-44.JIAQiu-peng,JIADong,ZHUAi-lan,et al.2007.Active tectonics in the Longmen thrust belt to the eastern Qinghai-Ti-beltan plateau and Sichuan basin:evidence from topography and seismicity[J].Chinese Journal of Geology,42(1):31-44(in Chinese).
李传友,宋方敏,冉勇康.2004.龙门山断裂带北段晚第四纪活动性讨论[J].地震地质,26(2):248-258.LI Chuan-you,SONG Fang-min,RAN Yong-kang.2004.Late Quaternary activity and age constraint of the northernLongmenshan Fault zone[J].Seismology and Geology,26(2):248-258(in Chinese).
李勇,曹叔尤,周荣军,等.2005.晚新生代岷江下蚀速率及其对青藏高原东缘山脉隆升机制和形成时限的定量约束[J].地质学报,79(1):28-37.LI Yong,CAO Shu-you,ZHOU Rong-jun,et al.2005.Late Cenozoic Minjiang incision rate and its constraint on the up-lift of the eastern margin of the Tibetan Plateau[J].Acta Geologica Sinica,79(1):28-37(in Chinese).
李勇,周荣军,Densmore A L.等.2006a.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,26(1):40-52.LI Yong,ZHOU Rong-jun,Densmore A L,et al.2006a.Geomorphic evidence for the late Cenozoic strike-slipping andthrusting in Longmen Mountains at the eastern margin of the Tibetan Plateau[J].Quaternary Sciences,26(1):40-52(in Chinese).
李勇,周荣军,Densenorea Ellism,等.2006b.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.LI Yong,ZHOU Rong-jun,Densenorea Ellism,et al.2006b.Geodynamic Processes of Eastern Margion of the TibetanPlateau and its Geological Responses[M].Geological Publishing House,Beijing(in Chinese).
刘树根,罗志立,赵锡奎,等.2003.龙门山造山带-川西前陆盆地系统形成的动力学模式及模拟研究[J].石油实验地质,25(5):432-438.LIU Shu-gen,LUO Zhi-li,ZHAO Xi-kui,et al.2003.Study on the dynamic mode and its simulation in the formation ofLongmen Mountain-West Sichuan foreland basin system[J].Petroleum Geology&Experiment,25(5):432-438(in Chinese).
马保起,苏刚,侯治华,等.2005.利用岷江阶地的变形估算龙门山断裂带中段晚第四纪滑动速率[J].地震地质,27(2):234-242.MA Bao-qi,SU Gang,HOU Zhi-hua,et al.2005.Late Quaternary slip rate in the central part of the Longmenshan Faultzone from terrace deformation along the Minjiang River[J].Seismology and Geology,27(2):234-242(in Chi-nese).
王阎昭,王恩宁,沈正康,等.2008.基于GPS资料约束反演川滇地区主要断裂现今活动速率[J].中国科学(D辑),38(5):582-597.WANG Yan-zhao,WANG En-ning,SHEN Zheng-kang,et al.2008.GPS monitoring of temporal deformation of theXianshuihe Fault[J].Science in China(Ser D),51(9):1259-1266DOI:10·3724/SP·J.1005·00225.
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 zones cuttinglate Quaternary stratum[J].Seismology and Geology,21(4):341-345(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.XUZhi-qin,LI Hua-qi,HOULi-wei,et al.2007.Uplifting of Longmen Shan and Jinping Shan,eastern margin of the Ti-betan Plateau:large scale detachment faults and their extrusion mechanism[J].Geol Bull China,26(10):1262-1276(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).
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 Pei-zhen,XU Xi-wei,WEN Xue-ze,et al.2008.Slip rates and recurrence intervals of the Longmenshan activefault zone,and tectonic implications for the mechanism of the May12Wenchuan earthquake,2008,Sichuan,China[J].Chinese Journal of Geoghysics,51(4):1066-1073(in Chinese).
周荣军,李勇,Alexander L D,等.2006.青藏高原东缘活动构造[J].矿物岩石,26(2):40-51.ZHOU Rong-jun,LI Yong,Alexander LD,et al.2006.Active tectonics of the eastern margin of the Tibet Plateau[J].Journal of Mineralogy and Petrology,26(2):40-51(in Chinese).
Densmore A L,Michael A,et al.2007.Active tectonics of the Beichuan and Pengguan Faults at the eastern margin ofthe Tibetan Plateau[J].Tectonics,26:doi:10·1029/2006TC001987.
陈桂华,徐锡伟,郑荣章,等.2008.2008年汶川MS8·0地震地表破裂变形定量分析:北川-映秀断裂地表破裂带[J].地震地质,30(3):723-738.CHEN Gui-hua,XU Xi-wei,ZHENG Rong-zhang,et al.2008.Quantitative analysis of the co-seismic surface rupture ofthe2008Wenchuan earthquake,Sichuan,China:along the Beichuan-Yingxiu Fault[J].Seismology and Geology,30(3):723-738(in Chinese).
陈社发,邓起东,赵小麟,等.1994.龙门山中段推覆构造带及相关构造的演化历史和变形机制[J].地震地质,16(4):404-421.CHEN She-fa,DENG Qi-dong,ZHAO Xiao-lin,et al.1994.Evolutionary history and deformation mechanism of centralLongmenshan thrust-nappes and related tectonics[J].Seismology and Geology,16(4):404-421(in Chinese).
邓起东,陈社发,赵小麟.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):389-403.DENG Qi-dong,CHEN She-fa,ZHAO Xiao-lin.1994.Tectonics,scismisity and dynamics of Longmenshan Mountainsand its adjacent regions[J].Seismology and Geology,16(4):389-403(in Chinese).
何宏林,孙昭民,王世元,等.2008.汶川MS8·0地震地表破裂[J].地震地质,30(2):359-362.HE Hong-lin,SUN Zhao-min,WANG Shi-yuan,et al.2008.Rupture of theMS8·0Wenchuan earthquake[J].Seis-mology and Geology,30(2):359-362(in Chinese).
贾秋鹏,贾东,朱艾斓,等.2007.青藏高原东缘龙门山冲断带与四川盆地的现今构造表现:数字地形和地震活动证据[J].地质科学,42(1):31-44.JIAQiu-peng,JIADong,ZHUAi-lan,et al.2007.Active tectonics in the Longmen thrust belt to the eastern Qinghai-Ti-beltan plateau and Sichuan basin:evidence from topography and seismicity[J].Chinese Journal of Geology,42(1):31-44(in Chinese).
李传友,宋方敏,冉勇康.2004.龙门山断裂带北段晚第四纪活动性讨论[J].地震地质,26(2):248-258.LI Chuan-you,SONG Fang-min,RAN Yong-kang.2004.Late Quaternary activity and age constraint of the northernLongmenshan Fault zone[J].Seismology and Geology,26(2):248-258(in Chinese).
李勇,曹叔尤,周荣军,等.2005.晚新生代岷江下蚀速率及其对青藏高原东缘山脉隆升机制和形成时限的定量约束[J].地质学报,79(1):28-37.LI Yong,CAO Shu-you,ZHOU Rong-jun,et al.2005.Late Cenozoic Minjiang incision rate and its constraint on the up-lift of the eastern margin of the Tibetan Plateau[J].Acta Geologica Sinica,79(1):28-37(in Chinese).
李勇,周荣军,Densmore A L.等.2006a.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,26(1):40-52.LI Yong,ZHOU Rong-jun,Densmore A L,et al.2006a.Geomorphic evidence for the late Cenozoic strike-slipping andthrusting in Longmen Mountains at the eastern margin of the Tibetan Plateau[J].Quaternary Sciences,26(1):40-52(in Chinese).
李勇,周荣军,Densenorea Ellism,等.2006b.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.LI Yong,ZHOU Rong-jun,Densenorea Ellism,et al.2006b.Geodynamic Processes of Eastern Margion of the TibetanPlateau and its Geological Responses[M].Geological Publishing House,Beijing(in Chinese).
刘树根,罗志立,赵锡奎,等.2003.龙门山造山带-川西前陆盆地系统形成的动力学模式及模拟研究[J].石油实验地质,25(5):432-438.LIU Shu-gen,LUO Zhi-li,ZHAO Xi-kui,et al.2003.Study on the dynamic mode and its simulation in the formation ofLongmen Mountain-West Sichuan foreland basin system[J].Petroleum Geology&Experiment,25(5):432-438(in Chinese).
马保起,苏刚,侯治华,等.2005.利用岷江阶地的变形估算龙门山断裂带中段晚第四纪滑动速率[J].地震地质,27(2):234-242.MA Bao-qi,SU Gang,HOU Zhi-hua,et al.2005.Late Quaternary slip rate in the central part of the Longmenshan Faultzone from terrace deformation along the Minjiang River[J].Seismology and Geology,27(2):234-242(in Chi-nese).
王阎昭,王恩宁,沈正康,等.2008.基于GPS资料约束反演川滇地区主要断裂现今活动速率[J].中国科学(D辑),38(5):582-597.WANG Yan-zhao,WANG En-ning,SHEN Zheng-kang,et al.2008.GPS monitoring of temporal deformation of theXianshuihe Fault[J].Science in China(Ser D),51(9):1259-1266DOI:10·3724/SP·J.1005·00225.
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 zones cuttinglate Quaternary stratum[J].Seismology and Geology,21(4):341-345(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.XUZhi-qin,LI Hua-qi,HOULi-wei,et al.2007.Uplifting of Longmen Shan and Jinping Shan,eastern margin of the Ti-betan Plateau:large scale detachment faults and their extrusion mechanism[J].Geol Bull China,26(10):1262-1276(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).
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 Pei-zhen,XU Xi-wei,WEN Xue-ze,et al.2008.Slip rates and recurrence intervals of the Longmenshan activefault zone,and tectonic implications for the mechanism of the May12Wenchuan earthquake,2008,Sichuan,China[J].Chinese Journal of Geoghysics,51(4):1066-1073(in Chinese).
周荣军,李勇,Alexander L D,等.2006.青藏高原东缘活动构造[J].矿物岩石,26(2):40-51.ZHOU Rong-jun,LI Yong,Alexander LD,et al.2006.Active tectonics of the eastern margin of the Tibet Plateau[J].Journal of Mineralogy and Petrology,26(2):40-51(in Chinese).
Densmore A L,Michael A,et al.2007.Active tectonics of the Beichuan and Pengguan Faults at the eastern margin ofthe Tibetan Plateau[J].Tectonics,26:doi:10·1029/2006TC001987.
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