西南深切河谷区滑坡早期识别及斜坡微地貌动态演化特征研究——以北川县白什乡老街后山滑坡为例

The Research of Early Identification of Landslide and Dynamic Evolution of Slope Microtopography in Deep Valley of Southwest China--A Case Study of the Landslide in the Ancient Street of Baishi Township, Beichuan County

我国西南深切河谷区,新构造运动活跃,地质环境条件复杂,滑坡灾害易发、频发,并具有较强的隐蔽性与突发性,该文以白什乡老街后山滑坡为例,利用七期遥感卫星数据对滑坡的早期变形特征、成因机制、运动模式以及后期演化特征进行分析研究。分析认为该地区斜坡早期变形特征表现为:①斜坡表部早期发育多条有序分布的形变裂缝;②斜坡相似部位发育并行排列且运动方向一致的早期小规模崩塌、滑坡等异常变形;③斜坡局部变形范围与斜坡早期裂缝,共同呈现出"近似圈闭"的边界形态特征;④构造方面,滑坡周边出露的较大规模断层,是该滑坡边界范围的控制条件之一,滑坡后缘与断层位置具有一定的吻合度;⑤微地貌特征方面,滑坡多发育于斜坡坡度突变的转折部位,临空条件好。上述特征可以作为该区域滑坡早期识别解译标志,其中①、②、③可以作为早期识别的直接解译标志,④和⑤作为间接解译标志或综合解译标志。在斜坡微地貌演化方面,该区域斜坡呈现出"斜坡后部早期裂缝形变"-"斜坡中部中期失稳,形成滑坡"-"坡脚堆积体,后期表部流水侵蚀形成冲沟"-"冲沟下切拉槽-泥石流二次堆积形成扇状堆积"的微地貌演化过程。

In the deep valley of southwest China, due to active neotectonic movement and complex geological environment, it is prone to frequently occur the landslide disaster, which is convert and abrupt.Taking the landslide in the ancient street of Baishi township as an example, the thesis, based on remote sensing satellite data during the seven-stage, will make a research of the early deformation characteristics, genetic mechanism, movement mode and later evolution features of the landslide.The analysis shows that the early deformation characteristics of the slope in this area are as follows:(1) Several deformation fractures in ordered distribution developed on the surface of the slope in the early stage.(2) Some abnormal deformation including early small-scale collapse and landslide occurred in similar parts of the slope in parallel arrangement with the same movement direction.(3) The local deformation range of the slope and the early crack of it present the boundary morphological characteristics of "approximate trap".(4) In terms of structure, the large-scale fault exposed around the landslide, as one of the control conditions of the landslide boundary range, coincides with the trailing edge of the landslide in view of the location.(5) In the aspect of microgeomorphologic features, landslides are mostly developed at the turning point of abrupt slope changes with good air conditions.The above features can be regarded as early identification and interpretation indicators of landslides in the region, among which(1),(2) and(3) can be used as direct interpretation indicators of early identification while(4) and(5) as indirect interpretation indicators or comprehensive interpretation indicators.In regard to slope microgeomorphic evolution, the slope in the region presents an evolutionary process of early-stage fracture deformation at the back of the slope-mid-stage instability in the middle of the slope forming a landslide-the slope pile deposits eroded by surface water at the later stage becoming a gully-gully cutting through the broached groove-the secondary accumulation of debris flow forming a fan-like accumulation.