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2008年5月12日在龙门山映秀-北川断裂带发生的8.0级特大地震,属于逆冲—走滑型地震。本文以地表破裂为切入点,在映秀-北川断裂的关键部位开展了详细的野外地貌测量,标定了映秀-北川断裂带的垂向断距和水平断距,结果表明映秀-北川断裂的地表破裂带从映秀向北东延伸达180～190km,走向介于NE30°～50°之间,倾向北西,地表平均垂向断距为2.9m,平均水平断距为3.1m;地表最大错动量的地点位于北川县擂鼓镇,垂直断错为6.2±0.1m,水平断错为6.8±0.2m,逆冲分量与右行走滑分量的比值为3∶1～1∶1,表明该断裂以逆冲—右行走滑为特点,逆冲运动分量略大于或等于右行走滑运动分量。根据近南北向的分段断裂可将映秀-北川断层的地表破裂带划分为两个高值区和两个低值区,其中两个高值区分别位于南段的映秀—虹口一带和中北段的擂鼓—北川县城—邓家坝一带。基于保存于破裂面上的擦痕,我们将该地震破裂过程划分为两个阶段,早期为逆冲作用,晚期为斜向走滑作用。
May 12, 2008 Longmenshan Yingxiu - Beichuan fault zone 8.0 magnitude earthquake, a thrust-strike-slip earthquake. In this paper, the surface rupture is taken as the starting point, and detailed field geomorphology measurements are conducted on the key parts of the Yingxiu-Beichuan fault. The vertical fault and horizontal fault of the Yingxiu-Beichuan fault zone are calibrated. The results show that the surface rupture of the Yingxiu-Beichuan fault The belt extends from Yingxiu to the north east by 180-190km with a trend of NE30 ° -50 °, with a northwestward tendency. The average vertical ground fault is 2.9m and the average horizontal fault is 3.1m. Located in Leigu town, Beichuan county, the vertical fault fault is 6.2 ± 0.1m and the horizontal fault fault is 6.8 ± 0.2m. The ratio of thrust component to right-hand slip component is 3: 1 ~ 1: 1, indicating that the fault is thrust - right-slip, characterized by a slightly greater or equal thrust component than the right-hand slip component. The surface rupture zone of Yingxiu-Beichuan fault can be divided into two high-value areas and two low-value areas according to the nearly north-south fault faults. Two high-value areas are located in the Yingxiu-Hongkou area and the north Leigu section - Beichuan County - Dengjiaba area. Based on the scratches preserved on the rupture surface, we divided the rupture process into two phases: early stage thrusting and late stage oblique strike-slip.