Abstract: 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.

Key words: M_S8.0 Wenchuan earthquake, the Beichuan-Yingxiu Fault, co-seismic surface rupture, deformation survey

摘要： 2008年汶川M_S8.0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。

关键词: 汶川M_S8.0地震, 北川-映秀断裂, 同震地表变形, 测量