Abstract. Coseismic landslides can destroy buildings, dislocate roads, sever pipelines, and cause heavy casualties. It is thus important but challenging to accurately map the hazards posed by coseismic landslides. Newmark's method is widely applied to assess the permanent displacement along a potential slide surface and model the coseismic response of slopes. This paper proposes an improved Newmark analysis for mapping the hazards of coseismic landslides by considering the roughness and effect of the size of the potential slide surfaces. This method is verified by data from a case study on the 2014 Mw 6.1 (the United States Geological Survey) Ludian earthquake in Yunnan Province, China. Permanent displacements due to the earthquake ranged from 0 to 122 cm. The predicted displacements were compared with a comprehensive inventory of landslides triggered by the Ludian earthquake to map the spatial variation in the hazards of coseismic landslides using the certainty factor model. The confidence levels of coseismic landslides indicated by the certainty factors ranged from −1 to 0.95. A hazard map of the coseismic landslide was generated based on the spatial distribution of values of the certainty factor. A regression curve relating the predicted displacement and the certainty factor was drawn, and can be applied to predict the hazards of coseismic landslides for any seismic scenario of interest. The area under the curve was used to compare the improved and the conventional Newmark analyses, and revealed the improved performance of the former. This mapping procedure can be used to predict the hazards posed by coseismic landslides, and provide guidelines for decisions regarding the development of infrastructure and post-earthquake reconstruction.
Forty-six ancient Tibetan star-shaped towers and a village are located on a giant slope, which would be partially flooded by a nearby reservoir currently under construction. Ground survey, boreholes, and geophysical investigations have been carried out, with results indicating that the slope consists of loose deposit with a mean thickness of approximately 80 m in addition to an overlying bedrock of micaceous schist and phyllite. Ground survey and Interferometric Synthetic Aperture Radar (InSAR) indicated that the slope is experiencing some local deformations, with the appearance of cracks and occurrence of two small landslides. Through using borehole logs with the knowledge of the regional geological background, it can be inferred that the loose deposit is a result of an ancient deep-seated translational landslide. This landslide was initiated along the weak layer of the bedding plane during the last glaciation in the late Pleistocene (Q 3 ) period, which was due to deep incision of the Dadu River at that time. Although it has not shown a major reaction since the ancient Tibetan star-shaped towers have been built (between 200 and 1600 AD), and preliminary studies based on geological and geomorphological analyses incorporated with InSAR technology indicated that the landslide is deformable. Furthermore, these studies highlighted that the rate of deformation is gradually reducing from the head to the toe area of the landslide, with the deformation also exhibiting relationships with seasonal rainstorms. The state of the toe area is very important for stabilizing a landslide and minimizing damage. It can be expected that the coming impoundment of the reservoir will increase pore pressure of the rupture zone at the toe area, which will then reduce resistance and accelerate the deformation. Future measures for protection of the slope should be focused on toe erosion and some bank protection measures (i.e., rock armor) should be adopted in this area. Meanwhile, some long-term monitoring measures should be installed to gain a deep understanding on the stability of this important slope.
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