四川汶川8.0级地震地表破裂与震害特点
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摘要
2008年5月12日四川汶川8.0级地震发生在青藏高原东缘的龙门山构造带上。通过野外实地调查与测量发现,汶川8.0级地震的地表破裂发生在龙门山构造带中的北川—映秀断裂之映秀南西—平武南坝石坎子段,彭县—灌县断裂的都江堰向峨—安县桑枣段也同时发生了同震地表破裂。北川—映秀断裂上的地表破裂长约220 km,表现为逆冲–右旋走滑运动特征,最大同震位错在6 m左右,水平与垂直位错量大致相当,与先期的研究成果一致;彭县—灌县断裂上的同震地表破裂长约100 km,表现为右旋–逆冲运动特征,最大垂直位错在2 m左右,水平与垂直位错量之比为1∶1～1∶3。地震地表破裂的空间分布及同震位错特征表明,汶川8.0级地震系北川—映秀断裂的逆冲–右旋运动所导致,并同时牵动了彭县—灌县断裂发生同震地表破裂。地震灾害的特点主要表现为地震波导致的强地面运动破坏、地震地表破裂带直接撕裂、地震导致的次生地质灾害(如崩塌和滑坡等)摧毁或掩埋建(构)筑物和堰塞湖等。根据地震考察资料并参考InSAR和强震仪记录,勾绘的该次地震等震线长轴方向沿龙门山构造带呈N40°～50°E方向延伸,出现了3个XI度的破坏区,具单侧多点瞬间破裂的典型特征,导致了四川北部、甘肃和陕西南部地区灾害较正常地震衰减破坏的显著加重。
On May 12 of 2008t,he Wenchuan M8.0 earthquake in Sichuan Province occurred on the Longmenshan tectonic belt at the eastern margin of the Qinghai—Tibet Plateau.Through field investigation and survey,the major surface rupture occurred on the segment of Beichuan—Yinxiu fault from the southwest of Yingxiu to Shikanzi of Nanba in Pingwu County,with a length of 220 km.It shows the fault produces a thrust and dextral slip.The maximum displacement along the fault is about 6 m;horizontal component is equivalent to the vertical direction.Another segment from Xiange in Dujiangyan City to Sangzao in Anxian County produces a 100 km coseismic surface rupture in length,also displaying a thrust and dextral characteristic of the fault.The maximum vertical displacement on this segment is about 2 m;and the ratio of the vertical component and the horizontal is between 1∶3 and 1∶1.The distribution of surface rupture and the characteristics of coseismic displacements show that the thrust-dextral slip of Beichuan—Yingxiu fault led to the Wenchuan M8.0 earthquake,representing strong ground motion destroy,surface cracking directly and secondary geological hazards(such as landslip,hillside creep) pulling down or burying the civic structures.Based on macroscopical surveys,tudies of InSARa,nd records of seismographs,the axis of isoseismal line extends at N40°–50°E orientation along the Longmenshan tectonic belt.Its typical characteristic is a unilateral,multipoint instantaneous rupture.The earthquake produced three intensity damaged areas with seismic magnitude XI,and remarkably enhanced the damages of normal earthquake attenuation in the North Sichuan province,the South Gansu Province and Hanzhong region of Shaanxi Province.
On May 12 of 2008t,he Wenchuan M8.0 earthquake in Sichuan Province occurred on the Longmenshan tectonic belt at the eastern margin of the Qinghai—Tibet Plateau.Through field investigation and survey,the major surface rupture occurred on the segment of Beichuan—Yinxiu fault from the southwest of Yingxiu to Shikanzi of Nanba in Pingwu County,with a length of 220 km.It shows the fault produces a thrust and dextral slip.The maximum displacement along the fault is about 6 m;horizontal component is equivalent to the vertical direction.Another segment from Xiange in Dujiangyan City to Sangzao in Anxian County produces a 100 km coseismic surface rupture in length,also displaying a thrust and dextral characteristic of the fault.The maximum vertical displacement on this segment is about 2 m;and the ratio of the vertical component and the horizontal is between 1∶3 and 1∶1.The distribution of surface rupture and the characteristics of coseismic displacements show that the thrust-dextral slip of Beichuan—Yingxiu fault led to the Wenchuan M8.0 earthquake,representing strong ground motion destroy,surface cracking directly and secondary geological hazards(such as landslip,hillside creep) pulling down or burying the civic structures.Based on macroscopical surveys,tudies of InSARa,nd records of seismographs,the axis of isoseismal line extends at N40°–50°E orientation along the Longmenshan tectonic belt.Its typical characteristic is a unilateral,multipoint instantaneous rupture.The earthquake produced three intensity damaged areas with seismic magnitude XI,and remarkably enhanced the damages of normal earthquake attenuation in the North Sichuan province,the South Gansu Province and Hanzhong region of Shaanxi Province.
引文
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[2]KIRBY E,WHIPPLE K X,TANG We,t al.Distribution of active rock uplift along the eastern margin of the Tibetan Plateau:Inferences from bedrock channel longitudinal profiles[J].Journal of Geophysical Research,2003,108(B4):2217,doi:10.1029/2001JB000861.
[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.(ZHOU Rongjun,LI Yong,DENSMORE A L,et al.Active tectonics of the eastern margin of the Tibet Plateau[J].Journal of Mineralogy and Petrology,2006:26(2):40–51.(in Chinese))
[4]ZHOU R J,LI Y,DENSMORE A L,et al.Active tectonics of the Longmenshan region on the eastern margin of the Tibetan Plateau[J].Acta Geologica Sinica,2007,81(4):593–604.
[5]DENSMORE A L,ELLIS M A,LI Y,et al.Active tectonic of the Beichuan and Pengguan faults at the eastern margin of the Tibetan Plateau[J].Tectonics,2007,26(4):TC4005.
[6]CHEN S F,WILSON C J L,DENG Q D,et al.Active faulting and block movement associated with large earthquakes in the Min Shan and Longmen Mountains,northeastern Tibetan Plateau[J].Journal of Geophysical Research,1994,99(B12):20 025–24 038.
[7]李勇,曾允孚,伊海生,等.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.(LI Yong,ZENG Yunfu,YI Haisheng,et al.Sedimentary record and tectonic evolution of Longmenshan foreland basin[M].Chengdu:Chengdu University of Science and Technology Press,1995.(in Chinese))
[8]AVOUAC J P,TAPPONNIER P.Kinematic model of active deformation in central Asia[J].Geophysical Research Letters,1993,20(10):895–898.
[9]ZHANG P Z,SHEN Z K,WANG M,et al.Continuous deformation of the Tibetan Plateau from global positioning system data[J].Geology,2004,32(9):809–812.
[10]ENGLAND P,MOLNAR P.Right-lateral shear and rotation as the explanation for strike-slip faulting in eastern Tibet[J].Nature,1990,344:140–142.
[11]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.(LI Yong,ZHOU Rongjun,DENSMORE A L,et al.Continental dynamic processes and geological response in the eastern margin of the Qinghai—Tibet Plateau[M].Beijing:Geological Publishing House,2006.(in Chinese))
[12]唐荣昌,韩渭宾.四川活动断裂与地震[M].北京:地震出版社,1993.(TANG Rongchang,HAN Weibin.Active faults and earthquakes in Sichuan Province[M].Beijing:Earthquake Press,1993.(in Chinese))
[13]陈国光,计凤桔,周荣军,等.龙门山断裂带第四纪活动性分段的初步研究[J].地震地质,2007,29(3):657–673.(CHEN Guoguang,JI Fengji,ZHOU Rongjun,et al.Primary research on activity segmentation of the Longmenshan fault zone since late Quaternary[J].Seismology and Geology,2007,29(3):657–673.(in Chinese))
[14]中华人民共和国国家标准编写组.GB18306–2001中国地震动参数区划图[S].北京:中国标准出版社,2001:1–2.(The National Standards Compilation Group of People′s Republic of China.GB18306–2001 The zonation map of earthquake ground motion parameters in China[S].Beijing:Standards Press of China,2001:1–2.(in Chinese))
[15]中华人民共和国国家标准编写组.GB50011–2001建筑抗震设计规范[S].北京:中国建筑工业出版社,2001.(The National Standards Compilation Group of People′s Republic of China.GB50011–2001 Code for seismic design of buildings[S].Beijing:China Architecture and Building Press,2001.(in Chinese))
[16]谢毓寿,蔡美彪.中国地震历史资料汇编(第1卷)[M].北京:科学出版社,1983:105–107.(XIE Yushou,CAI Meibiao.Compilation of historical data of earthquakes in China(Volume 1)[M].Beijing:Science Press,1983:105–107.(in Chinese))
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