Abstract:

A seven magnitude earthquake occurred in Lushan County, Yaan City, Sichuan Province on April 20, 2013, which caused 193 deaths or missing and with a loss amounting to RMB 1.4 billion. The structure of mountains, rock and soil was severely damaged by the Lushan earthquake, which induced a series of geological disasters including landslide, collapse, debris flow and so on. The serious geological disasters threatened the life, the property of the local people, the significant infrastructure and even the ecological condition. Exhaustive study and hazard assessment of debris flow in Lushan earthquake were of important realistic significance. Using the AHP method, we selected six assessment factors, namely terrain slope, lithology, fracture zone, vegetation cover, earthquake intensity and annual rainfall. In the application of AHP method, the weight of each factor was determined. The weight is 0.186 for seismic intensity, is 0.284 for rainfall factor, 0.176 for slope, 0.169 for lithology, 0.108 for fracture zone, and 0.077 for vegetation cover. The study area was eventually classified into five categories (extremely low, low, moderate, high, extremely high), which were determined according to the views of experts as well as the understanding of the regional development of geological hazards. Grade 1 to 5 were used to indicate the different hazard levels. Grade 5 represented the most dangerous, while Grade 1 represented the least dangerous. The choice of GIS technology for spatial analysis completed the study using the weighted superposition model. Applying the spatial analysis tool in GIS, a zoning map of debris flow hazard assessment was obtained. The result showed a regular pattern that the study area such as Lushan County, Tianquan County, Mingshan District, and Yucheng District located in the extremely high hazard area, and its level of hazard zoning was mainly affected by the earthquake and rainfall factors. We draws a conclusion that the division of the study area and the feature of geological hazard point distribution were in substantial agreement.