Morphology and inner structure of Luanshibao rock avalanche in Litang,China and its implications for long-runout mechanisms
Morphology and inner structure of Luanshibao rock avalanche in Litang,China and its implications for long-runout mechanisms
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理塘乱石堡岩崩的形态、内部结构及其长期运行机制的意义
DOI：
10.1016/j.enggeo.2019.105216
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发表时间：
2019
影响因子：
7.4
通讯作者：
Liye Liao
中科院分区：
文献类型：
--
作者：
Qingli Zeng;Luqing Zhang;Tim Davies;Guangxiang Yuan;Xinyu Xue;Rongqiang Wei;Qianfeng Yin;Liye Liao
大型岩石雪崩通常移动迅速，移动距离很长，使其非常危险，并经常导致灾难性的破坏。目前提出的关于导致其高流动性的机制的假设仍然存在争议（Petley，2013）。乱石堡古花岗岩崩落体跨立塘活动断裂，其~（10）Be暴露年龄为3510±346年B. P.，存款量为67 Mm ~ 3。它行驶了大约4000米，表观摩擦系数为0.22。通过野外调查、卫星图像解译、存款的形态和内部结构研究，分析了其运动学和动力学特征，并探讨了其长期跳动机理。研究结果表明，由于次生陡坎的发育和裸露岩块的发育，可能存在从岩坡崩塌到岩屑扩散的两阶段运动过渡。跳动量与次级陡坎脱落的体积密切相关。识别出三种不同类型的存款形态，即，平行的横向脊槽，X槽和菱形平台，和圆椭圆形的丘，从近端到远端，分别表示由于压缩，剪切和拉伸运动的碎片中的应力的应变响应。这些存款形态以及内部结构，如块体的均匀层，内部剪切带和锯齿状破碎块，建议额外的跳动碎片作为“层流”或“流片”的模式移动。然而，强烈的混合河流卵石和雪崩碎片在远端丘区建议的模式“湍流”。强烈地震引起的饱和河流沉积物液化、基底中岩屑高速不排水剪切产生的额外孔隙压力和大量第四纪沉积物的夹带，可能导致基底摩擦力的大幅降低。粒度随远离次级陡坎而减小，锯齿状结构解体，表明岩石破碎发生在运动过程中。这表明，岩石雪崩的长时间运行是多种因素共同作用的结果。
Large rock avalanches usually move rapidly and travel long distances, making them extremely hazardous, and often result in catastrophic damages. The currently proposed hypotheses for the mechanisms causing their high mobility remain controversial (Petley, 2013). The Luanshibao ancient granite rock avalanche, with a 10Be exposure age of 3510±346 years B.P. and a deposit volume of 67 Mm3, straddles on the Litang active fault and was deposited on an open-flat river terrace without confinement. It traveled about 4000 m, with an apparent coefficient of friction of 0.22. Field investigation, interpretation of satellite images, and study of the morphology and inner structure of its deposit were used to analyze its kinetics and dynamics, and its long runout mechanisms..The study showed that there was probably a two-stage movement transition from rock-slope collapsing to debris spreading, based on the remarkable high secondary scarps and a long belt of bare blocks. The runout is closely related to the volume detached from the secondary scarp. Three different kinds of deposit morphologies were recognized, i.e., parallel transverse ridge-grooves, X grooves and rhombic platforms, and round-elliptical hummocks, from the proximal to the distal end, indicating the strain response to stresses in the debris in motion due to compression, shear and tension, respectively. These deposit morphologies as well as the inner structures such as homogeneous layers of blocks, inner shear belts and jigsaw fractured blocks, suggested that the extra runout debris moved as a pattern of “laminar-flow” or as a “flow-sheet”. However, the strong mixing of fluvial pebbles and avalanche debris in the distal hummocky zone suggested a pattern of “turbulent flow”. The possible liquefaction of saturated fluvial sediments by a triggering strong earthquake, the extra pore pressure generated by the high-speed undrained shearing of debris in the substrate and the entrainment of a large amount of Quaternary sediment, could have contributed to the great reduction of friction of the basal layer. The particle size decreasing with distance away from the secondary scarps and the disintegration of jigsaw structures, suggest that rock fragmentation occurred during motion. This implies that the long runout of the rock avalanche resulted from many factors..