2008年汶川M_S8.0地震地表破裂变形定量分析——北川-映秀断裂地表破裂带
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摘要
2008年汶川MS8.0地震在北川-映秀断裂产生了长达240km的同震地表破裂。通过详细的测量、基于测量标志与断裂变形的几何关系对数据的分析,给出了观测点的断裂同震地表变形的垂直位移、倾向水平缩短、走向滑动、断层上盘水平运动方向等参数。结果显示,断裂同震变形分布的空间变化很大,目前获得的最大水平位移位于虹口乡深溪沟,为4.98m,同时也是最大右旋走滑位移点,走滑量4.5m,而目前获得的最大垂直位移在其东北的支沟,为5.7~6.7m。NE向断裂水平位移多为1~2m,垂直位移多为3m左右,而小鱼洞-草坝分支断裂水平位移和垂直位移都更小,只有0.5~1.5m。擂鼓镇附近的数据则反映与断裂相关的巨型滑坡可能将重力变形叠加到构造变形中。由断层水平缩短和垂直位移计算的断层倾角表明,北川-映秀断裂是浅部陡倾的具有走滑分量的逆断层。
A 240km-long co-seismic surface rupture was produced along the Beichuan-Yingxiu Fault during the 2008 Wenchuan earthquake.We made a detailed survey at representative sites along the surface rupture and analyzed the data based on the geometry between the benchmark and deformation.The co-seismic vertical slip,horizontal dip-slip shortening,strike slip and moving direction of the hanging-wall were calculated based on the survey data of these sites.Results show that the spatial distribution of the co-seismic deformation of the fault varies a lot along the fault.The maximal horizontal slip,as we got till now,is located in the Shenxigou site of Hongkou with a value of 4.98m,and the maximal strike slip is also located in the same site with a value of 4.5m.The maximal vertical displacement is located to the northeast of Shenxigou with a value of 5.7～6.7m.The average horizontal slip for the NE trending fault is 1～2m,and the average vertical slip is 3m.But horizontal and vertical slip for the NW-trending branch from Xiaoyudong to Caoba is only 0.5～1.5m.The data from Leigu town show that the gravity deformation resulting from the fault-related landslide was perhaps superimposed on the tectonic one.The dip angles of the fault at the surveyed sites calculated from the horizontal shortening and vertical displacement indicate that the Beichuan-Yingxiu Fault is a steep dipping reverse fault with some strike-slip.From the comparison between field results and geophysical inversion,we believe that the spatial distribution of co-seismic fault-slip is related to the barriers and rupture process along the fault plane.
A 240km-long co-seismic surface rupture was produced along the Beichuan-Yingxiu Fault during the 2008 Wenchuan earthquake.We made a detailed survey at representative sites along the surface rupture and analyzed the data based on the geometry between the benchmark and deformation.The co-seismic vertical slip,horizontal dip-slip shortening,strike slip and moving direction of the hanging-wall were calculated based on the survey data of these sites.Results show that the spatial distribution of the co-seismic deformation of the fault varies a lot along the fault.The maximal horizontal slip,as we got till now,is located in the Shenxigou site of Hongkou with a value of 4.98m,and the maximal strike slip is also located in the same site with a value of 4.5m.The maximal vertical displacement is located to the northeast of Shenxigou with a value of 5.7～6.7m.The average horizontal slip for the NE trending fault is 1～2m,and the average vertical slip is 3m.But horizontal and vertical slip for the NW-trending branch from Xiaoyudong to Caoba is only 0.5～1.5m.The data from Leigu town show that the gravity deformation resulting from the fault-related landslide was perhaps superimposed on the tectonic one.The dip angles of the fault at the surveyed sites calculated from the horizontal shortening and vertical displacement indicate that the Beichuan-Yingxiu Fault is a steep dipping reverse fault with some strike-slip.From the comparison between field results and geophysical inversion,we believe that the spatial distribution of co-seismic fault-slip is related to the barriers and rupture process along the fault plane.
引文
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陈运泰,许力生,张勇,等.2008.2008年5月12日汶川特大地震震源特性分析报告[R].http:∥www·csi·ac·cn/sichuan/chenyuntai·pdf.CHEN Yun-tai,XU Li-sheng,ZHANG Yong,et al.2008.report on the great Wenchuan earthquake source of May12,2008[R].http:∥www·csi·ac·cn/sichuan/chenyuntai·pdf(in Chinese).
王卫民,姚振兴.2008.再谈汶川8·0级地震震源破裂过程[R].http:∥www·csi·ac·cn/sichuan/sichuan080512_110.htm.WANG Wei-min,YAO Zhen-xing.2008.Reissues for the rupture process of theMS8·0Wenchuan earthquake[R].http:∥www·csi·ac·cn/sichuan/sichuan080512_110.htm(in Chinese).
徐锡伟,陈文彬,于贵华,等.2002.2001年11月14日昆仑山库赛湖地震(MS8·1)地表破裂带的基本特征[J].地震地质,24(1):1-13+133-136.XU Xi-wei,CHENWen-bin,YUGui-hua,et al.2002.Characteristic features of the surface ruptures of the Hoh Sai Hu(Kunlunshan)earthquake(MS8·1),northern Tibetan Plateau,China[J].Seismology and Geology,24(1):1-13+133-136(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).
中国地震信息网.2008.四川汶川县MS8·0地震参数[R].http:∥www·csi·ac·cn/sichuan/sichuan080512_cs1.htm.China Seismic Information Net.2008.Seismological parameters for theMS8·0Wenchuan earthquake,Sichuan[R].http:∥www·csi·ac·cn/sichuan/sichuan080512_cs1.htm(in Chinese).
朱艾斓,徐锡伟,刁桂苓,等.2008.汶川MS8.0地震部分余震重新定位及地震构造初步分析[J].地震地质,30(3):759-767.ZHU Ai-lan,XU Xi-wei,DIAO Gui-ling,et al.2008.Relocation of theMS8·0wenchuan earthquake sequence in part:preliminary seismotectonic analysis[J].Seismology and Geology,30(3):759-767(in Chinese).
Ji C,Hayes G.2008.Preliminary result of the May12,2008MW7·9Eastern Sichuan,China earthquake[R].http:∥earthquake·usgs·gov/eqcenter/eqinthenews/2008/us2008ryan/finite_fault·php.
Sladen A.2008.Preliminary result05/12/2008(MW7·9),East Sichuan[R].http:∥www·tectonics·caltech·edu/slip_history/2008_e_sichuan/e_sichuan·htm.
USGS.2008.Magnitude7·9-Eastern Sichuan,China[R].http:∥neic·usgs·gov/neis/eq_depot/2008/eq_080512_ryan.
Xu X W,Yu G H,Y Klinger,et al.2006.Reevaluation of surface rupture parameters and faulting segmentation of the2001Kunlunshan earthquake(MW7·8),northern Tibetan Plateau,China[J].Journal of Geophysical Research-Solid Earth,111(B5):Doi10·1029/2004jb003488.
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