汶川八级地震滑坡特征分析

FEATURES OF LANDSLIDES TRIGGERED BY THE WENCHUAN EARTHQUAKE

汶川地震诱发的15000多处滑坡明显受地震断裂控制,主要沿龙门山主中央断裂带和后山断裂带展布,沿龙门山主中央断裂带汶川映秀—安县高川—北川陈家坝—平武南坝一线,滑坡面密度大于50%以上,最大可达70%。沿断裂带形成了大量的松动山体,在暴雨期间极易发生滑坡、泥石流灾害,对灾后重建构成严重威胁。据初步调查,汶川地震触发的体积最大的滑坡是位于主中央断裂带上的安县高川大光包滑坡,滑动距离长4500m,滑坡堆积体长2800m,宽1700～2200m,最大厚度达580m,若以平均厚度200m计,体积达11亿m3,为我国已发生的单体滑坡之最。与常见滑坡明显不同的是,汶川地震极震区滑坡的滑床往往不具连续完整的滑面,剪出口滑坡特征不明显,呈现明显的"尖点突起"或"边缘突出"特征,反映出上部滑体被地震力振动解体,甚至抛掷后与下部滑床边缘发生撞击。以阶型滑坡、凸型滑坡、勺型崩滑、座落型(振胀型)滑坡和巨大滚石5种类型最为典型。根据强震地面运动纪录和大量实例调查表明,在汶川地震极震区,触发滑坡的地震竖向力作用是非常明显的,大量滑坡经历了初始斜坡(风化碎裂岩体)——地震抛掷——撞击崩裂——高速滑流的作用过程。

Over 15,000 landslides were triggered by the Wenchuan Earthquake along the Main seismic fault and back fault of the Longmen Mt. tectonic belt. The area density of landslide coverage, i. e. , the ratio of the landslide distribution and total area, is greater than 50 % in average and 70% in maximum along the Yingxiu - Gaochuan - Chenjiaba - Nanba of the main seismic fault. The enormous loosen rock masses easy for occurring landslides and debris flows will seriously threat the reconstruction and living, especially, during raining seasons. The largest landslide triggered by the Wenehuan Earthquake is located at the Daguangbao, Anxian County, of the main seismic fault. The volume of the Daguangba landslide is 1. 1 billion m3, and 4,500 m long from scarp to toe, 2,800 m long, 1,700 to 2,200 m wide and 200 m in average thickness, and 580 m in max thickness for accumulation. It is also the maximum volume of single landslide in China. Much differences with other conventional landslides, the sliding surfaces are common incomplete and discontinued, and the exits were unclear in the epicenter area of the Wenehuan Earthquake, which illustrates the upper rock mass was strongly vibrated and separated, then thrown and crushed with the bedrock. The five patterns of the landslides are classified as staircase - shaped, convex - shaped, bowel - shaped, slump （ vibrated - expansive ） - shaped and huge rock -stone in a broad sense. The strong ground motion records and destroyed house cases present that the vertical seismic load is dominated within the epicenter area, i. e. , the vertical is greater than the horizontal of seismic load. It provides an explanation why lots of landslides experienced the processes of broken - thrown - crushed -high speed debris flow.