茂县滑坡的滑动机制与震后滑坡形成的地质条件

Sliding mechanism of Maoxian landslide and geological condition analysis of formation of post-earthquake landslide

2017年6月24日在四川茂县新磨村发生高位巨型滑坡,是汶川地震后所发生的规模最大的一次岩质滑坡,滑坡体积巨大,破坏性强,造成了巨大的损失。基于现场调查资料和搜集的相关资料,描述了茂县滑坡的几何形态特征和沉积物特征,初步探讨了该区降雨条件、历史地震、活动断裂等特征及其对滑坡发生的影响,提出了茂县滑坡的滑动机制和动力学机制。主要成果包括:(1)茂县滑坡所在的富贵山处于松坪沟断裂和岷江断裂交汇和夹持的区域,显示为挤压型高陡(微)地貌,并具有"X"形平面断裂组合样式和"背冲式"剖面组合样式。(2)该区经历了多次强烈历史地震的影响,反复强烈的震动及叠加、累积变形破坏了岩体结构、坡面结构,降低了岩石的内聚力、摩擦强度和斜坡岩体的稳定性,并导致该区滑坡降雨阈值的降低,表明活动断裂及其历史地震是驱动茂县滑坡形成的主要控制因素,而降雨仅为诱发因素。(3)茂县滑坡的滑动模式为顺层拉裂-顺坡滑脱型模式,滑动过程可分为山体裂解阶段、高速溃滑阶段、碎屑流堆积阶段。在此基础上,提出了茂县滑坡的成因机制,主要表现在:高陡的单面山斜坡(顺层、顺坡)的临空条件是滑坡产生的势能条件;贯通性好的变质砂岩与板岩之间的滑动面(层面)是滑坡形成顺层拉裂-顺坡滑脱的滑动条件;富贵山两侧活动断裂对该山体的挤压抬升以及多次高强度历史地震的震动、变形的积累及其对岩体结构的长期破坏,是导致滑坡产生的地质条件。

On June 24,2017,a large rocky landslide occurred at the Xinmo village,Maoxian County,Sichuan,after the Wenchuan earthquake in 2008.The landslide is huge and destructive,resulting in huge loss of life and property.Based on the field survey data and other collected data,the geometric characteristics and sedimentary characteristics of the Maoxian landslide are studied,the characteristics and effect of rainfall,historical earthquakes and active faults on the landslides are discussed,and the sliding mechanism and dynamic mechanism of Maoxian landslide are proposed.The study reveals that the landslide is located in the special area clamped by Songpinggou fault and the Minjiang fault with a steep slope landform and the faults are characterized by ＂X＂pattern in the plane with a back thrust mode in the profile.Investigation shows that intense historical earthquakes have occurred in the area and the strong repetitive vibration destroyed the rock mass structures.Therefore,the active faults and historical earthquakes in the area are the main factors responsible for the formation of the Maoxian landslides,and the rainfall is only the predisposing factors trigger the landslides.The in site investigation also demonstrates that the sliding model of Maoxian landslide is characterized by layer parallel pull-apart together with slope parallel sliding.These are 3stages in the formation processes of Maoxian landslide,beginning with the mountain rock cracking stage,then the high speed crushing stage and followed by debris flow accumulation stage.The steep slope and downward grade provide potential energy for the landslide.Well developed permeability interface between meta-sandstone and slate provide sliding condition bringing in the layer parallel pull-apart and slope parallel sliding.The fault compression induced uplift of Fugui Mountain,together with the accumulation of high-intensity historical earthquake vibration and accumulation of deformation,which resulted in long-term damage to the mountain rock structure,are the fundamental factors leading to the Maoxian landslide.