2008年5月12日汶川地震(Ms8.0)地表破裂带的分布特征
摘要
2008年5月12日14时28分,青藏高原东缘龙门山地区(四川汶川)发生了Ms8.0级地震。震后野外考察表明,5.12汶川地震发生在NE走向的龙门山断裂带上,该断裂带晚新生代以来的逆冲速率小于1mm/a,GPS观察结果表明其缩短速率小于3mm/a。这次5.12汶川地震造成了多条同震逆冲地表破裂带,总体长约275km,宽约15km,发震断裂机制主要为逆冲作用(由NW向SE逆冲)伴随右旋走滑。地表主破裂带沿龙门山断裂带的映秀—北川断裂发育,长约275km,笔者称为映秀—北川破裂带,破裂带具有逆冲兼右旋走滑性质。地表次级破裂带沿龙门山断裂带的前缘断裂安县—灌县断裂南段发育,长80km,笔者称为汉旺破裂带,破裂带基本为纯逆冲性质。在这两条破裂带之间发育两条更次一级的同震地表破裂带:一条长约20km呈NE走向的地表破裂带,笔者称为深溪沟破裂带,由于这条破裂带靠近主破裂带南段,并且与主破裂带变形特征一致,因此,笔者将深溪沟破裂带划归映秀—北川破裂带;另一条长约6km呈NW走向、由SW向NE逆冲并兼有左旋滑动的地表破裂带,笔者称为小鱼洞破裂带,它连接映秀—北川破裂带和汉旺破裂带,成为侧向断坡。另外,在灌县—安县断裂东侧的四川盆地内,由都江堰的聚源到江油发育一条NE向的沙土液化带,它可能是四川盆地西部深部盲断裂活动的结果。同震地表破裂带的分布特征表明,龙门山断裂带活动断裂具有强烈的逆冲作用并伴随较大的右旋走滑,断裂向四川盆地扩展。在龙门山断裂带上类似2008年5月12日Ms8.0汶川大地震的强震复发周期为3000~6000a。
On May 12, 2:28 pm, an earthquake (Ms 8.0) struck the Longmenshan area (centred in Wenchuan County of Sichuan Province), the eastern segment of the Tibetan Plateau. According to the field survey, the earthquake occurs on the NE striking Longmenshan fault belt. The belt has been with the thrusting rate smaller than 1 mm/a and the shortening rate smaller than 3 mm/a according to GPS measurement. The causative mechanism is mainly the thrust (from NW to SE), accompanied with dextral strike-slip. The earthquake produced several co-seismic surface rupture zones that were 275 km long and 15 km wide in general. The Yingxiu-Beichuan rupture zone is 275 km long and dominative;The Hanwang rupture zone takes the second place, which is 70 km long and occurs along the south part of the Guanxian-Anxian fault, the frontal fault of the Longmenshan fault belt. There are another two minor rupture zones between two zones mentioned above, one is the Shenxigou rupture zone, is in NE direction and about 10 km long, close to the southern segment of the main rupture zone, whose deformation characteristics are similar to and can be involved into the Yingxiu-Beichuan rupture zone; the other is named as Xiaoyudong rupture zone, is in NW direction and 6 km long, produced by the thrust from SW to NE and associated lateral slip, which is the link between Yingxiu-Beichuan and Hanwang rupture zone and characterized by the lateral ramp. Besides, in the Sichuan Basin that eastern to the Guanxian-Anxian fault, a sand liquefaction belt with NE direction strike developed from Juyuan town of Dujiangyan to Jiangyou, which might be the result of the activity of a blind fault deep in the western Sichuan Basin. According to the feature of surface coseismic rupture zones, active tectonics in the Longmenshan fault belt have intense thrusting accompanied with significant dextral strike-slip. The fault is developing toward the Sichuan Basin. The recurrence intervals of great earthquake such as the Wenchuan earthquake can be 3000-6000 years.
On May 12, 2:28 pm, an earthquake (Ms 8.0) struck the Longmenshan area (centred in Wenchuan County of Sichuan Province), the eastern segment of the Tibetan Plateau. According to the field survey, the earthquake occurs on the NE striking Longmenshan fault belt. The belt has been with the thrusting rate smaller than 1 mm/a and the shortening rate smaller than 3 mm/a according to GPS measurement. The causative mechanism is mainly the thrust (from NW to SE), accompanied with dextral strike-slip. The earthquake produced several co-seismic surface rupture zones that were 275 km long and 15 km wide in general. The Yingxiu-Beichuan rupture zone is 275 km long and dominative;The Hanwang rupture zone takes the second place, which is 70 km long and occurs along the south part of the Guanxian-Anxian fault, the frontal fault of the Longmenshan fault belt. There are another two minor rupture zones between two zones mentioned above, one is the Shenxigou rupture zone, is in NE direction and about 10 km long, close to the southern segment of the main rupture zone, whose deformation characteristics are similar to and can be involved into the Yingxiu-Beichuan rupture zone; the other is named as Xiaoyudong rupture zone, is in NW direction and 6 km long, produced by the thrust from SW to NE and associated lateral slip, which is the link between Yingxiu-Beichuan and Hanwang rupture zone and characterized by the lateral ramp. Besides, in the Sichuan Basin that eastern to the Guanxian-Anxian fault, a sand liquefaction belt with NE direction strike developed from Juyuan town of Dujiangyan to Jiangyou, which might be the result of the activity of a blind fault deep in the western Sichuan Basin. According to the feature of surface coseismic rupture zones, active tectonics in the Longmenshan fault belt have intense thrusting accompanied with significant dextral strike-slip. The fault is developing toward the Sichuan Basin. The recurrence intervals of great earthquake such as the Wenchuan earthquake can be 3000-6000 years.
引文
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[12]张培震,徐锡伟,闻学泽,等.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,2008,51(4):1066-1073.Zhang Peizhen,Xu Xiwei,Wen Xueze,et al.Slip rates and recurrence intervals of the Longmen Shan active fault zone,and tectonic implications for the mechanism of the May12Wenchuan earthquake,2008,Sichuan,China[J].Chinese Journal Of Geophysics,2008,51(4):1066-1073(in Chinese with English abstract).
[13]Zhou R J,Li Y,Densmore A L,et al.Active tectonics of the Longmen shan region on the eastern margin of the Tibetan plateau[J].Acta Geologica Sinica,2007,81(4):593-604.
[14]Burchfiel B C,Royden L H,van der Hilst R D,et al.A geological and geophysical context for the Wenchuan earthquake of12May2008,Sichuan,People's Republic of China[J].GSA Today,2008,18(7):doi:10.1130/GSATG18A.1.
[2]陈运泰,许力生,张勇,等.2008年5月12日汶川特大地震震源特性分析报告[R].2008.Chen Yuntai,Xu Lisheng,Zhang Yong,et al.Analysis of the source parameters of the great Wenchuan earthquake of May12,2008[R].2008.
[3]Ji et al.http://www.geol.ucsb.edu/faculty/ji/big_earthquakes/2008/05/12/Sichuan.html.
[4]邓起东.中国活动构造研究[J].地质论评,1996,42(4):295-299.Deng Qidong.Active tectonics in China[J].Geological Review,1996,42(4):295-299(in Chinese with English abstract).
[5]许志琴,李化启,侯立炜,等.青藏高原东缘龙门-锦屏造山带的崛起—大型拆离断层和挤出机制[J].地质通报,2007,26(10):1262-1276.Xu Zhiqin,Li Huaqi,Hou Liwei,et al.Uplift of the Longmen-Jinping orogenic belt along the eastern margin of the Qinghai-Tibet Plateau:Large-scale detachment faulting and extrusion mechanism[J].Geological Bulletin of China,2007,26(10):1262-1276(in Chinese with English abstract).
[6]许志琴,侯立玮,王宗秀,等.中国松潘-甘孜造山带的造山过程[M].北京:地质出版社,1992:1-190.Xu Zhiqin,Hou Liwei,Wang Zhongxiu,et al.Orogenic Process of the Songpan-Ganzi Orogen in China[M].Beijing:Geological Publishing House,1992:1-190(in Chinese with English abstract).
[7]王二七,孟庆任,陈智梁,等.龙门山断裂带印支期左旋走滑运动及其大地构造成因[J].地学前缘,2001,8(2):375-384.Wang Erqi,Meng Qingren,Chen Zhiliang,et al.Early Mesozoic left-lateral movement along the Longmen shan fault belt and its tectonic implications[J].Earth Science Frontiers,2001,8(2):375-384(in Chinese with English abstract).
[8]李勇,周荣军,Densmore A L,等.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,2006,26(1):40-52.Li Yong,Zhou Rongjun,Densmore A L,et al.Geomorphic evidence for the late Cenozoic strike-slipping and thrusting in Longmen mountain at the eastern margin of the Tibetan plateau[J].Quaternary Sciences,2006,26(1):40-52(in Chinese with English abstract).
[9]Densmore A L,Ellis M A,Li Y,Active tectonics of the Beichuan and Pengguan faults at the eastern margin of the Tibetan Plateau[J].Tectonics,2007,26,doi:10.1029/2006TC001987.
[10]唐荣昌,韩渭宾(主编).四川活动断裂与地震[M].北京:地震出版社,1993:1-368.Tang Rongchang,Han Weibin.Active faults and earthquake in Sichuan Province[M].Beijing:Seismlolgical Press,1993:1-368(in Chinese).
[11]冯先岳.新疆古地震[M].乌鲁木齐:新疆科技卫生出版社,1997:1-250.Feng Xianyue.Palaeo-earthquakes of Xinjiang[M].Urumqi:Science&Technology and Health Publishing House,1997:1-250(in Chinese).
[12]张培震,徐锡伟,闻学泽,等.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,2008,51(4):1066-1073.Zhang Peizhen,Xu Xiwei,Wen Xueze,et al.Slip rates and recurrence intervals of the Longmen Shan active fault zone,and tectonic implications for the mechanism of the May12Wenchuan earthquake,2008,Sichuan,China[J].Chinese Journal Of Geophysics,2008,51(4):1066-1073(in Chinese with English abstract).
[13]Zhou R J,Li Y,Densmore A L,et al.Active tectonics of the Longmen shan region on the eastern margin of the Tibetan plateau[J].Acta Geologica Sinica,2007,81(4):593-604.
[14]Burchfiel B C,Royden L H,van der Hilst R D,et al.A geological and geophysical context for the Wenchuan earthquake of12May2008,Sichuan,People's Republic of China[J].GSA Today,2008,18(7):doi:10.1130/GSATG18A.1.
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