青藏高原东缘理塘乱石包高速远程滑坡发育特征与形成机理

Huge long-runout landslide characteristics and formation mechanism:A case study of the Luanshibao landslide,Litang County,Tibetan Plateau

青藏高原复杂的地质构造背景，导致该区地震频发，加之该区异常的气候变化，大型乃至巨型地质灾害发育多，危害大。在遥感解译、野外地质调查、物探、槽探和地质测年资料分析的基础上，论述了乱石包滑坡的发育特征，并对其形成机理进行分析探讨。认为乱石包高速远程滑坡具有如下特征：①乱石包滑坡的滑动方向垂直于理塘－德巫断裂的北西段，乱石包滑坡顶部接近于现代雪线；②乱石包滑坡最大滑行距离达3.83km，滑坡后壁与前缘堆积区的高差约820m，滑体方量0.64×108~0.94×108m3，平均滑动速度约53.25m/s；③测年资料表明，乱石包滑坡形成1980±30aBP左右；④组成滑坡体的岩性主要为花岗岩，在长期构造活动和冷冻风化作用下，节理裂隙发育，呈碎裂岩体。分析表明，乱石包滑坡受断裂构造、地形地貌和古气候变化影响较大，形成机理复杂：①理塘－德巫断裂全新世以来活动强烈，具有强震地质背景，由该断裂活动形成的强震可能是乱石包滑坡形成的主要因素之一，在地震作用下，坡顶部地震波放大，垂直加速度大于水平加速度，岩体发生震胀和抛掷，从而形成高速远程滑动；②距今1800~2000aBP左右时，青藏高原地区的温度变化较大，该时期发生的大规模冰川活动可能是乱石包滑坡发生的主要因素之一；③地震、气候变化的组合也是引起乱石包滑坡发生的成因之一，并形成一个完整的地质灾害链：地震→雪崩→岩崩→高速碎屑流。

In the Tibetan Plateau, the complex geological tectonic background causes frequent earthquakes, together with the abnor?mal climate change, there are many large or even huge geological hazards, causing serious consequences. In this paper, based on theinterpretation of remote sensing and the analysis of field geological survey, geophysical prospecting, trenching, and geological dating data, the authors studied the development characteristics of the Luanshibao landslide and investigated its formation mechanism. TheLuanshibao long-runout landslide has the following features: ① The Luanshibao landslide is located on the northeastern margin ofthe Maoyaba Basin in Litang County, western Sichuan. The sliding direction of the landslide is perpendicular to the northwesternsegment of the Litang-Dewu fault, with the top part of the Luanshibao landslide approaching the current snow line. ②The maxi?mum sliding distance of the Luanshibao landslide is 3.83km; the elevation difference between the back wall of the landslide and theaccumulation zone at the leading edge is approximately 820m, with a sliding body volume of approximately 0.64×108~0.94×108m3and an average sliding velocity of approximately 53.25m/s. ③ The dating data indicate that the Luanshibao landslide occurred atabout 1980±30a BP. ④ The compositional lithology of the landslide rocks is mainly granite, and the joint fractures are developed ascracked rocks under the impact of long-term tectonic dynamics and freezing weathering. The analysis indicates that the Luanshibaolandslide has been substantially affected by the fault structure, terrain topography, and ancient climate change, and its formationmechanism is complicated: ① Since the Holocene, the Litang-Dewu fault has experienced frequent, strong earthquake activity. Thestrong earthquakes resulting from the fault activity might have been one of the main factors for the formation of the Luanshibaolandslide. Under the impact of earthquakes, the seismic wave at the top of the slope would be "amplified", producing a vertical accel?eration greater than the horizontal acceleration. The rock bodies experienced shock expansion and were thrown, forming the longrunoutlandslide. ② Dating back to approximately 2000a BP, the temperature change in the Tibetan Plateau area was relativelylarge, and the large-scale glacial activity occurring in this period was most likely one of the main factors behind the formation of theLuanshibao landslide. ③ The combination of earthquakes and climate change seems to have been one of the conditions causing theoccurrence of the Luanshibao landslide, forming a complete chain of geological disasters, i.e., earthquake→avalanche→rockfall→high speed debris flow.