Spatial structure characteristics and formation mechanism of the ancient Deda landslide elucidated using the microtremor survey method in Sichuan Province,China
[Objective]The topography and geological structure of the eastern Qinghai-Tibet Plateau are highly complex.High development density and intricate spatial structures of large ancient landslides in alpine canyon areas,such as those in the Jinsha River,contribute to this complexity.In addition,hazards resulting from creep deformation and the resurgence of these ancient landslides are severe.The ancient Deda landslide,situated in Deda Township,Batang County,Sichuan Province,is a significant ancient landslide influenced by the Chalong-Ranbu fault activity.The spatial structural characteristics of this ancient landslide are complex,with localized resurgence deformation at the landslide front.[Methods]Various methods were included in the current study,such as remote sensing interpretation,on-site investigations,the microtremor survey method(MSM),and engineering geological drilling to elucidate further the spatial structural characteristics of the ancient Deda landslide.[Results]The research revealed that the ancient Deda landslide can be divided into three sections in the plan view:the Deda I landslide(I),the Deda II landslide(II),and the rear wall of the ancient Deda landslide(Ⅲ).Using MSM combined with drilling verification,a scheme for classifying the shear wave velocities of shallow and deep sliding zones was constructed,with a relative error in sliding zone depth identification ranging 2.6%～4.8%.This paper showed that the Deda I landslide features two sliding zones,with a burial depth of 18.7～20.1 m for the shallow sliding zone(S1-1)and 36.2～49.9 m for the deep sliding zone(S1-2).The volume of the Deda I landslide is approximately 8.7×106～12.0×106 m3.The Deda II landslide has one sliding zone(S2)with a 25.2～38.6 m burial depth and a landslide volume of approximately 6.3×106～9.6×106 m3.[Conclusion]A comprehensive analysis suggested that the formation of the ancient Deda landslide was the result of various factors,including fault structures,rainfall infiltration,and river erosion.The complex landslide structure and its genesis were identified as the primary controlling factors for landslides in a state of creep deformation.[Significance]The research methods and insights presented in this study can serve as a reference for the spatial identification and risk prevention of large ancient landslides on the eastern Qinghai-Tibet Plateau.
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