Abstract: During the M_S 8.0 Wenchuan earthquake,most of surface deformation zones show as flexural scarps or fault scarps,and surface ruptures in bedrock are rare.However,earthquake surface ruptures are entirely exposed in bedrock and discovered by authors near Xiaojiaqiao town of Anxian county.Based on careful analysis of the deformation characteristics and the inner structure of this rupture zone,and in combination with features of the regional earthquake surface ruptures,the authors hold that the earthquake surface ruptures are developed and extend mainly along the preexisting Yingxiu-Beichuan Fault during this earthquake,the faulting is right-reverse-slip movement at a low angle,and the maximum vertical co-seismic dislocation is 5.4 meters,which coincide with the measurements of the flexural scarps or fault scarps.

Key words: M_S 8.0 Wenchuan earthquake, surface rupture in bedrock, the Yingxiu-Beichuan Fault, co-seismic dislocation, right-reverse-slip movement

摘要： 在汶川M_S 8.0地震中,地表破裂变形带多表现为挠曲坎或断层坎,地表基岩破裂少见,作者在安县肖家桥附近基岩中发现了出露完整的地震地表破裂带。在仔细分析该破裂带变形特征和内部结构构造的基础上,结合区域上地震地表破裂特点,认为:这次地震的地表破裂主要沿先存的映秀-北川断裂发生和扩展,地震断层作用形式以右旋斜冲运动为主,安县肖家桥附近映秀-北川断裂的最大垂直同震位错为5.4m,与通过挠曲坎或断层坎测量的结果基本一致。

关键词: 汶川M_S 8.0地震, 基岩地表破裂, 映秀-北川断裂, 同震位错, 右旋斜冲运动