0016-7622/2013-82-5-575/$ 1.00 © GEOL. SOC. INDIA JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.82, November 2013, pp.575-582 Pre-conditioning Factors and Susceptibility Assessments of Wenchuan Earthquake Landslide at the Zhouqu Segment of Bailongjiang Basin, China SHIBIAO BAI 1 , QIANG XU 2 , JIAN WANG 1 and PINGGEN ZHOU 3 1 College of Geographical Sciences, Key Laboratory of Virtual Geographic Environments (National Education Administration), Nanjing Normal University, Nanjing, 210046 (China) 2 State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu Iniversity of Technology, Chengdu 610059, China; 3 China Institute of Geo-Environment Monitoring, Beijing, China Email: shibiaobai21@163.com Abstract: In this study, we present a landslide susceptibility assessment carried out after the devastating 2008 Wenchuan earthquake. For the Zhouqu segment in the Bailongjiang basin in north-western China landslide susceptibility was computed by a logistic regression method. This region has been experiencing landslides for a long time, and numerous additional slope failures were triggered by the 2008 Wenchuan earthquake. The data used for this study consists of slope failures attributed to the 2008 earthquake, the 878 post Wenchuan earthquake landslides and collapses inventory build up by combination the field investigation, monoscopic manual interpretation, image classification and texture analysis using SPOT 5 and ALOS remote-sensing image data. All data derived from remote sensing images are validated during field investigations. The landslide pre-disposing factor database was constructed. A digital elevation model (DEM) with a 30 x 30 m resolution, orthophotos, geological and land-use maps and information on peak ground acceleration data from the 2008 earthquake is used. The statistical analysis of the relation between Wencuan earthquake-triggered landslides and pre-disposing factors show the great influence of lithological and topographical conditions for earthquake-triggered slope failures. The quality of susceptibility mapping was validated by splitting the study area into a training and validation set. The prediction capability analysis showed that the landslide susceptibility map could be used for land planning as well as emergency planning by local authorities in this region. Keywords Landslide susceptibility, Wenchuan earthquake, Zhouqu segment, China. Landslide susceptibility is a quantitative or qualitative assessment of the classification, volume (or area), and spatial distribution of landslides which exist or potentially may occur in an area. Susceptibility may also include a description of the velocity and intensity of the existing or potential landslide (Fell et al. 2008). Both qualitative and quantitative methods have been used in the processes of creating landslide-susceptibility maps (Soeters and van Westen, 1996; Aleotti and Chowdhury, 1999; Guzzetti et al. 1999). The qualitative method was widely used during the late 1970s by engineering geologists and geo- morphologists. The quantitative methods, however, became popular in the last few decades largely because of its numerical expressions of the relationship between controlling factors and landslides, assisted by the advances in computer and geographic information system (GIS) technology (Guzzetti et al. 2005; van Westen et al. 2008; Bai et al. 2010b). The purpose of this study is to analyse the relation INTRODUCTION Nationwide the landslide related direct and indirect economic losses account for more than 2 billion euros every year (Hu and Tang, 2005). The Zhouqu-Wudu segment of the Bailongjiang basin in northwestern of China with a total area of 8,917 km² lies in the middle south of the west wing of Qinling orogen. It is controlled by Qinghai-Tibet tectonic belt and Wudu arc structure, and affected by uplift of the Qinghai-Tibet plateau. This segment is located in the Qinling mountains, and is surrounded by three major geomorphic units, namely, the Qinghai-Tibet plateau, the Loess plateau and the Sichuan basin. Because of its geophysical conditions, the Bailongjiang basin is one of the most severely affected regions in China by landslide (Scheidegger and Ai, 1987). There are more than 2,000 medium and large scale landslides (volume is greater than 3 × 10 4 m 3 ) within the Wudu and Zhouqu segment. In addition to the soft and erodable lithologic formations, the area is tectonically active, and has been frequently experiencing earthquakes.