Landslide hazards triggered by the 2008 Wenchuan earthquake, Sichuan, China
The 2008 Wenchuan earthquake (M s = 8.0; epicenter located at 31.0° N, 103.4° E), with a focal depth of 19.0 km was triggered by the reactivation of the Longmenshan fault in Wenchuan County, Sichuan Province, China on 12 May 2008. This earthquake directly caused more than 15,000 geohazards in the form of landslides, rockfalls, and debris flows which resulted in about 20,000 deaths. It also caused more than 10,000 potential geohazard sites, especially for rockfalls, reflecting the susceptibility of high and steep slopes in mountainous areas affected by the earthquake. Landslide occurrence on mountain ridges and peaks indicated that seismic shaking was amplified by mountainous topography. Thirty-three of the high-risk landslide lakes with landslide dam heights greater than 10 m were classified into four levels: extremely high risk, high risk, medium risk, and low risk. The levels were created by comprehensively analyzing the capacity of landslide lakes, the height of landslide dams, and the composition and structure of materials that blocked rivers. In the epicenter area which was 300 km long and 10 km wide along the main seismic fault, there were lots of landslides triggered by the earthquake, and these landslides have a common characteristic of a discontinuous but flat sliding surface. The failure surfaces can be classified into the following three types based on their overall shape: concave, convex, and terraced. Field evidences illustrated that the vertical component of ground shaking had a significant effect on both building collapse and landslide generation. The ground motion records show that the vertical acceleration is greater than the horizontal, and the acceleration must be larger than 1.0 g in some parts along the main seismic fault. Two landslides are discussed as high speed and long runout cases. One is the Chengxi landslide in Beichuan County, and the other is the Donghekou landslide in Qingchuan County. In each case, the runout process and its impact on people and property were analyzed. The Chengxi landslide killed 1,600 people and destroyed numerous houses. The Donghekou landslide is a complex landslide–debris flow with a long runout. The debris flow scoured the bank of the Qingjiang River for a length of 2,400 m and subsequently formed a landslide dam. This landslide buried seven villages and killed more than 400 people.
KeywordsWenchuan earthquake Landslide Landslide lake Rapid and long runout
After the 2008 Wenchuan earthquake, the authors participated in field investigations and mitigations of geohazards triggered by the earthquake for about 1 1/2 months, which was organized by the MLR. This paper is completed based on this work and the abundant collected data. The authors would like to sincerely thank Mr. Min Wang, the Deputy Minister of MLR, and Mr. Jianjun Jiang, the Director of Department of Environmental Geology of MLR, and Mr. Guangqi Song, the Director of Department of Land and Resources of Sichuan Province, Mr. Chongrong Fan, the Deputy Director of Geological Prospecting Bureau of Sichuan Province, Prof. Runqiu Huang, the Vice President of Chengdu University of Technology, and Mr. Jun Ding, the Director of Chengdu Center of China Geological Survey, for their support and help. The comments by Lynn Highland, Edwin Harp and Alexander Strom on this paper were highly appreciated.
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