RS-BASED EXTRACTION AND DISTRIBUTION CHARACTERISTICS OF GEO-HAZARDS TRIGGERED BY WENCHUAN EARTHQUAKE IN MIANYUAN RIVER BASIN

On May 12, 2008, a MS8.0 earthquake occurred in the Longmenshan fault zone in Sichuan province of China. It induced large amounts of geo-hazards. Comprehensive and accurate disasters catalog and the development pattern analysis are the foundation of research in disaster prevention and control. The Mianyuan river basin is one of the typical areas where seismic disasters well developed. This paper used two SPOT5 remote sensing images which took after the earthquake, combined with the aerial image took before the earthquake, automatically identified the geo-hazards spots and connected with the field investigation and visual check. It catalogued the slope geological disasters accurately. By comparison and contrast between the results of the previous researches in the study area and the method used in this paper, this geological disasters extraction method has a lot of advantages. The results are more completely and accurately. On the basis of the disaster development regularity of spatial analysis, we obtained some new understanding different from the previous ones. (1)Paying more attention to the choice and contrast of the times when RS images took and using RS image are an effective method for extraction of coseismic geological disasters, so as to obtain accurate and complete interpretation results; (2)the extracted area of disasters is 85.5km2,about two times the research by predecessors. Visual results show that the area of disasters mainly distribute in Beichuan-Yingxiu surface rupture zone and along the both sides of the Mianyuan river; (3)the main factors influencing the distribution of geological disasters in Wenchuan earthquake are elevation, slope, slope-shape, surface ruptures and stratigraphic lithology. Near the elevation of 1500m and 4100m, the geo-hazards area percentages are large, above 31% and 25%respectively. The distribution is positively related to the slope. The geo-hazards area percentage is mainly concentrated in the vicinity of 50. Disasters mainly distribute in the concave slope units, followed by convex slopes. The disasters have big relationships with the active faults complexity characteristics of activity in the region. On the hard rock or the soft stratums with hard under is the main sliding area of disasters, its area percentage up to 49.6%.