Application Of 3S Technology In The Sliding Mass Distribution Research In Ludian Earthquake

On 3rd August 2014, a 6.5-magnitude earthquake happened in Ludian County, Yunnan Province. The earthquake resulted in serious landslides in large scale, 617 deaths, 1088,400 citizens involved, and 80,900 houses demolished, which causes a lot of casualties and huge loss of fortune. The traditional method of identifying earthquake landslide is outdoor survey done by surveyors, which is extremely dangerous and slow, in need of a lot of manpower and materials. With the growing maturity of 3S technology, it can provide a powerful tool for geological disaster research with its strong geospatial information management and analysis function, which makes the geological disaster research reach a brand-new period with informatization, digitalization, and quantification. The application of rapidly-developing geospatial information system in geological disasters is obviously the best, the most economical and the most reasonable method to store, process, utilize, and present the information for disasters.This assay uses three methods based on 3S technology, namely Visual Interpretation, Vegetation Cover Rate, and D-InSAR. Visual Interpretation is to extract the sliding mass according to the characteristics of landslide with ArcGIS directly from high-resolution images and then calculate the area size. Vegetation Cover Rate is to get the vegetation cover rate in Ludian area from inversion of NDVI( Normalized Difference Vegetation Index). From the comparison and analysis for images before and after the earthquake, we find the areas with decreasing vegetation cover rates. The areas in valleys whose vegetation rates decrease is concluded with a combination of the steep slopes, which is landslide areas caused by the earthquake. D-InSAR technology is to generate interference images from phase information recorded in the two radar images before and after the earthquake. Then some of the phase for terrain and plain ground are removed with comparison with DEM data and inversion through some formulas follows. Finally the terrain deformation monitoring from the landslides will presented by terrain deformation date transferred from phase information.From the three methods above-mentioned, we receive three types of distribution of the landslides. Even though there is a slight difference in the area sizes conclude from them, the distribution direction goes mainly from northwest to southeast. The largest landslide is situated in Ganjiazhai village by the river bank of ShaBa River. And the second largest the Red Rock landslide to the right side of Niulan River, which blocks the river and forms a barrier lake.The land-sliding is related to the structure, types of rocks, and weathering status, etc. The distribution of different types of rocks is relatively regional. We can believe that the landslides in Ludian Earthquake are mainly caused by the structure status because the widely-spreading metamorphic rock from the Paleozoic Era, gypsiferous rock from the Mesozoic Era, and soft rocks from the Cenozoic Era in the area bring rocks that are broken, with varied hardness and low stability. The trend of the fault determines the distribution directions and density of the landslides, which from the date analysis for this case are mainly going from northwest to southeast. The conclusion is the seismogenic fault of M_S 6.5-magnitude earthquake in Ludian is a stream valley fault in Bao Gu Nao in the northwest direction.On the basis of the CF theory, in the consideration of the influence from terrain and water factor on the stability of landslide, we pick 6 impact factors and follow four steps, namely grading of factors, calculation of landslide area size within the factors, calculation of conditional probability, and calculation of CF value. We get an analysis chart on the stability of landslides from calculation. We find that Ludian area is mountainous and landslides tend to happen along the river banks and roads. In the areas that are relatively plain, the ground is relatively stable. This will form certain guidelines for after-disaster reconstruction.From analysis from this assay, there are three major conclusions:(1) Landslides of Ludian earthquake mainly go from northwest to southeast after analyzing the advantages and disadvantages for the three methods.(2) The trend of the seismogenic fault of Ludian earthquake and the distribution direction of the landslides correspond with each other, both in a stream fault in Bao Gu Nao.(3) The landslide areas in Ludian earthquake lie along the river banks and roads, which are relatively less stable. Therefore post-disaster reconstruction and so on need to keep away from those potential areas for disasters.