Assessment Of Debris Flow Susceptibility Potential In Lushan Earthquake Zone, China

As a common natural disaster, debris flows occur in mountainous basins frequently, and which often cause extremely severe loss of life and property. For a more accurate expression of the rich provenance and reliable debris flow-prone assessment result caused by Lushan earthquake, this paper will be carried out debrisflow susceptibility studies using certainty factor method and geomorphic information entropy method, based on geographic information system, remote sensing technology, geology method and statistics theory. We made the following key findings:(1) Combining visual interpretation and field survey verification, 453 mudslides small basins have been selected with a total area of approximately 4481.22 km2 in the study area.(2) Lushan earthquake triggered lots of landslide deposits, which often deposited on the slope or the slope angle. Response rate of seismic slope mass movement(RRSSMM) changed from 0 to 14.79 mm. More than 90 percent of the debris flow basins are landslide provenance insensitive because that low and very low degree sensitive area accounts for percent 91.84 of the total small basins area.(3) Some classes of the six predisposing factors(namely elevation, slope angle, slope aspect, geologic periods, lithology and NDVI) are prone to debris flows. Certainty factor method for debris flow distribution analysis shows as following:(1) debris flow susceptibility ranges are 2000 m and above of elevation; 20o and above of slope angle; north, south-east, east, south-east, south and north-west of slope aspect; Nanhua, Ordovician, etc. of geologic periods;-1~0.2 of NDVI; and these lithologies, namely limestone, dolomite and other carbonate rocks, and pyroclastic rocks etc. of these rocks outcropping area.(4) In order to obtain the most prone to debris flow combination of six environment factors, different factors combinations are introduced. In addition, we also need to examine the success rate of different combinations of the generated index map. The test results of the success rate show that the area under curve(AUC) of the combination of terrain, physiognomy and geological is percent 88.93, this combination has a more accurate assessment result of the debris flow-prone than other combinations.(5) Considering landslide provenance, the assessment results of the debris flow-prone based on certainty factor method show that debris flows were extremely inactive because moderate and above area accounts for percent 7.76 of the total small basins area.(6) The value of geomorphic information entropy changes from 0.0001 to 0.8976, which shows physiognomy evolution from childhood to old age. But physiognomy evolution from childhood to middle age still accounts for a large proportion. Height and above prone area is 4284.30km2, namely percent 49.25 of the study area, indicating that nearly half of the more active debris flow basins. However, if landslide provenance is introduced, moderate and above-prone area will be less than percent 5 indicating debris flow activity is not very active.