The Identification of Large-Giant Bedrock Landslides Triggered by Earthquake in the Longmenshan Tectonic Belt

The identification of large-giant bedrock landslides triggered by earthquake aims to the landslide prevention and control. Previous studies have described the basic characteristics, distribution, and the formation mechanism of seismic landslides （Bijan Khazai et al., 2003; Chong Xu et al., 2013; Lewis a. Owen et al., 2008; Randall W. Jibson et al., 2006）. However, few researches have focused on the early identification indicators of large-giant bedrock landslides triggered by earthquake （David k. Keefer., 1984; Janusz Wasowski et al., 2011; Alexander L.Strom., 2009; Patrick Meunier et al., 2008; Shahriar Vahdani et al., 2002; Bijan Khazai et al., 2003）. This paper presents the identification indicators of large-giant bedrock landslides triggered by earthquake in the Longmenshan tectonic belt on the basic of their characteristics, distribution and the relationship between seismic landslides and the peak ground motion acceleration.

Imaging the Western Boundary of the Sichuan Craton from Multiple Geophysical Observations

The boundary between cratonic and orogenic lithospheres is a significant seismogenic zones marked by intense lithospheric deformation.The Sichuan Craton(SCC),as a key tectonic block bordering eastern Tibetan Plateau,resists the eastward escape of plateau's crustal materials,resulting in the uplift of the Songpan-Ganzi Block(SGB)and crustal deformation of the Longmenshan tectonic belt(LMTB).To elucidate the compressional structures and deformational modes of the LMTB and SCC,it is essential to accurately determine the location and geometry of the SCC'western boundary.To investigate this issue,the lithospheric properties of the obducted SGB,underthrusting SCC,and LMTB were analyzed using various geophysical data,including seismic reflection profiles,magnetotellurics,aeromagnetics,gravity,and seismic tomography.The SGB crust is characterized by low magnetism,seismic velocity,resistivity and Bouguer gravity,whereas the SCC crust exhibits non-uniform high magnetism,seismic velocity,resistivity and Bouguer gravity.The LMTB,as the boundary between the SGB and SCC,exhibits geophysical characteristics similar to those of the SCC in the southern and central segments.The integration of these geophysical observations indicate that the SCC's western boundary is situated west of the Wenchuan-Maoxian fault zone in the southern and central segments,exhibiting distinct westward wedging and underthrusting.However,this boundary aligns with the Yingxiu-Beichuan fault in the northern segment,without significant underthrusting.The irregular geometry of the SCC's western boundary further elucidates the variation in structural deformation along the LMTB.By comparing crustal thickness and lithospheric strength between the SGB and SCC,this study posits that the differing crustal strength between tectonic blocks may control the irregular geometry of the SCC's western boundary.