【摘要】 2008年5月12日汶川M_s8.0级特大地震发生后,在北川县擂鼓地区出露了一条擂鼓同震地表破裂带,该破裂带呈近南北向展布,位于映秀-北川断裂的中北段,其北东起于擂鼓镇柳林村北部,南西止于石岩村南部,以脆性破裂为特征,分别由3条呈北北东、北西西、北北东走向的地表破裂组成,延伸长度约4～5km,并切割了多种地貌单元,其平均垂直断距为1.5m,平均水平断距为1.4m,垂直与水平断距之比为1.07:1。通过对该地表破裂带野外测量数据、几何展布结构及其成因机制的初步分析表明:擂鼓断裂是出露于擂鼓地区的捩断层,具有捩断层的基本特性;其主要特征包括:1)擂鼓断裂的形成是由于在汶川地震中其东西两侧逆冲块体之间的差异性运动而引起;2)断裂呈近南北向展布,与映秀-北川主干断裂近垂直相交;3)断面倾角较陡,为高角度断面的逆断层,具有逆冲兼走滑特征。更多还原

【Abstract】 The Ms8.0 serious earthquake occurred in Longmenshan（Longmen Mountain）on May 12^th ,2008 caused a new surface rupture named Leigu fault in the Leigu area（Leigu Town of Beichuan）. The Leigu fault is located between the north segment and south segment of the Yingxiu - Beichuan fault. We measured vertical and horizontal offsets of the Yingxiu- Beichuan fault and the Leigu fault by GPS and EDM in this area. The results show that the Leigu fault has fragile characteristics with approximately N-S striking,extending about 4 ～ 5km,and cutting various terrain units. The surface rupture of Leigu fault is complex,made up by three segments which are striking to NNE, NWW, and NNE from north to south in the Leigu area, respectively. Along the NNE striking of Leigu fault which is characterized by left lateral oblique in the north segment, its northwest block is a hanging wall and the southeast block is a foot wall with an average vertical offset of 1.7meters and an average horizontal offset of 1.3meters. When the Leigu fault strikes to NWW in the middle segment,which turns out to be characterized by right lateral oblique, its southwest block is a hanging wall and the northeast block is a foot wall with an average vertical offset of 1.3meters and an average horizontal offset of 1.5meters. In the south segment of the Leigu fault,the surface rupture strikes to NNE, with complicated topographic and geomorphologica features, e.g. Debris flow, landslide, cliff collapse,and so on. As a result the data of vertical and horizontal displacements are not capable currently. The average vertical and horizontal offsets of the north and middle segments are 1.5meters and 1.4meters. The ratio of the thrust component to strike-slip component is 1.07 : 1. According to the result of geomorphic surveys,the plane fabric pattern of the surface ruptures caused by the Wenchuan Earthquake in the Leigu area shows that the Leigu fault joins to the two paralleled thrust faults, both of which belong to the Yingxiu - Beichuan fault. The surface rupture pattern in the Leigu area shows that the Leigu fault was formed by differential movement of thrusting of the Longmenshan thrust zone during the Wenchuan Earthquake, striking to N-S direction which approximately is vertical to the strike of the Yingxiu - Beichuan fault, and dipping at high angles with thrust and strike-slip. As a result,the Leigu fault is a tear fault.更多还原