汶川八级地震滑坡高速远程特征分析

汶川地震触发的高速远程滑坡主要沿龙门山主中央断裂带汶川映秀安县高川北川县城平武南坝青川一线地震破裂带展布。由于获得了1.5g以上的抛掷加速度，具有明显的气垫效应，估计最大滑动速度一般大于70ms-1，滑动距离一般为滑体启动时长度的数倍甚至10多倍，堆积成坝形成多处堰塞湖，最大滑行距离达3.2km。本文重点解剖了位于地震破裂带南西段(初始震中)的汶川映秀牛圈沟滑坡碎屑流、位于地震破裂带中段的北川城西滑坡和位于地震破裂带北东段青川东河口滑坡碎屑流3个典型实例，认为具有如下特征:(1）岩性条件:母岩遭受长期构造动力作用，呈碎裂岩体，后期被强烈风化，岩体极为破碎；(2）抛掷效应:位于汶川地震主断裂带或附近，垂直加速度大于水平加速度，强地面运动持时长，岩体发生振胀和抛掷；(3）碰撞效应:上部滑坡体发生高位剪出和高位撞击，致使岩体碎屑化；(4）铲刮效应:撞击作用导致下部山体被铲刮，形成次级滑坡，为碎屑流体提供了足够展翼和抛洒物源体积；(5）气垫效应:碎屑化岩体快速抛掷导致下部沟谷空气迅速谷状圈闭和向下紊流，形成气垫效应，或者，在下部地形开阔地带压缩空气呈层流状态致使滑体凌空飞行。

RAPID AND LONG RUN-OUT FEATURES OF LANDSLIDES TRIGGERED BY THE WENCHUAN EARTHQUAKE

The extremely rapid and long run-out landslides triggered by the Wenchuan Earthquake were occurred along the Yingxiu-Gaochuan-Beichuan-Nanba-Qingchuan of the main seismic fault. The estimated maximum sliding velocity is greater than 70ms-1 under the over 1.5g earthquake acceleration, compared with conventional rainfall or liquefaction induced landslides. The run-out distance of landslide-debris is several or several ten times of the rockmass length from crown to exit due to the air layer lubrication in where lots of landslide dams occurred. The maximum run-out distance is 3200m. The three cases are studied from the Niuquangou rockslide-debris flow at the south west segment of the main seismic fault(Yingxiu, Wenchuan), the Chengxi rockslide at the middle segment of the main seismic fault (Beichuan) and the Donghekou rockslide-debris flow at the north east segment of the main seismic fault.The three cases illustrates following common characteristics: (1)parent rockmass is broken under long geologic processing and weathered; (2) Rockmass was separately expanded and thrown under long-period strong ground vibration in which the vertical motion was predominant along the main seismic fault; (3)sliding mass was crashed at the exiting zone and transferred to fragment material; (4) The secondary landslide was triggered underneath the exiting zone due to the powerful crashing and shaving processes that provides more mass to debris body and cushion shape；(5) The a long run-out distance fragment flow is occurred under air layer lubrication. The air layer was pressed and turbulently flowed in the narrow-shaped valley, or laminarly flowed in the extensive flatland.