Research Of Primarily Impact Factors Of Seismic Landslide At Shifang Mountain Area Based On GIS And RS

The landslide hazard is a kind of deteriorating geological environment caused by natural geological processes and human activities, its occurrence mainly includes internal factors and external effects, internal factors, including lithology, elevation, slope, aspect, and so on. external factors including rainfall, vegetation cover, human activities, and so on. Seismic landslide refers to gravitational geologic disasters including collapses, landslides and mudslides, when earthquake happening it induces slope deformation and instability under the influence caused by the seismic wave-vibration and gravity. The landslide frequently occurs in many parts of the world, and brings huge economic losses to people in disaster areas, results in heavy casualties. In order to prevent and reduce the harm caused by the landslide hazard, this paper selects the mountain area in Shifang City located on the Longmen Mountains Zhongshan fault zone as study area, use remote sensing images QuickBird data to get data of earthquake landslides. Combine GIS technology with RS technology,with information method, for landslide impact of single-factor analysis and the analysis of comprehensive impact weight, in order to get landslide hazard levels of the study area, and compare distributed characters of landslides in landslide hazard rating, and draw the following conclusions:1. Use remote sensing images QuickBird data (February2010) as basic data of earthquake landslides research. In order to obtain study area of remote sensing images QuickBird data about mountain area in Shifang City, splice the seven pictures of remote sensing QuickBird data, use the study area as clipping boundary, then get the study area remote sensing data, the study area is48686hm2,then make the image geometric correction to clipped remote sensing images in ERDAS, referencing to1:10000topographic map. and put calibrated images into Arc GIS, according to the standards of visual interpretation, finishing data extraction of landslide layer vectorization of study area, at last we get390landslides, the area is531.11hm2.2. Make DEM data as basic data to extract geographic information factors. First clip the DEM under clipping boundary of study area, get the same boundary to remote sensing images. With spatial statistics tool in Arc GIS, we can extract four geographic factors from DEM:that is elevation, slope, aspect, river. Reclassify the obtained geographic factors data to make each layer set normalized.3. According Sichuan Province geological map, finish vector quantization of geological map, get geological map of study area.4. Convert elevation, slope, aspect, river layer to raster type, and make the cell-size30×30. use zonal statistics tool in GIS use landslide layer and each factor layer to do analysis respectively, and calculate the homologous information value, compositively analyze and get the results:when the circumstances are elevation of2500-3000m,slope>60°. southeast aspect, the fourths lever of river level, the lithology arkose are the most vulnerable combination of factors to landslides; but when the elevation4000m,slop range0-10°. the ground aspect, the eighth level river, the lithology granodiorite, then the conditions are not the most prone areas to landslides.5. Make all factor layers to do raster calculation analysis, then combine GIS with information method, build the relevant model, and get the assessment map of landslide risk rating.6. Use "natural break point method" for the re-classification, at last divide the evolutional figure into five levels, are respectively the milder, mild, moderate, height, and heighter. the milder information range is-10.06～4.19,the mild information range is-4.19～-0.38, the moderate information range is-0.38～0.22,the height information range is0.22-0.32,the heighter information range is0.32～3.21.7. Do statistics about the ratio of landslide happening in reality(b/a, that is the landslide density in the rating at the percentage of the rating account for the study area), the milder rating b/a0.006808,the mild rating b/a0.686379,the moderate rating b/a1.254116,the height rating b/a1.379227,and the heighter rating b/a1.418099,the results indicate that with the ratio of landslide happening actually rising, and the risk rating increasing, that is it’s very feasible to use information method to assess the risk rating of landslide, the results are valid.