The Evaluating Of The Susceptibility About Geological Disaster In Langao County Based On GIS

Taking potential geological disasters from the geological disasters detailedinvestigation in Langao County as a subject for study in this thesis, on the basisof the field investigation, time-space distribution features, the formationconditions and the influencing factors on the potential geological disasters in thestudy area are made a detailed analysis. Combined with the current thought onsusceptibility zoning of geological disasters, susceptibility of geologicaldisasters in the study area is evaluated through using index method andinformation acquisition analysis. The findings are as follows:(1) There develop502potential geological disasters including440landslides,13collapses and49mudslides. Space distribution law of geologicaldisasters is that they exist all over the county with different development degreeand crowd together along the Lan River, Dadao River and their tributaries. Timedistribution law of geological disasters is that most of them happened in theperiod of intensive human engineering activity and during every monsoon sincethe Holocene. In addition, the major influencing factors on the formation of thegeological disasters are terrain, geological structure, rock type, ground-water, and mankind activities.(2) For susceptibility index method of geological disasters, the weights ofevaluation index are determined by analytic hierarchy process (AHP). Usingmathematics model of index method to calculate susceptibility index ofgeological disasters, and after statistic analysis of the susceptibility indexes ofall the units, these indexes are overlaid through natural breaks. The zoningboundaries,2.5413and1.1763are obtained through natural breaks and thesusceptibility degree of each assessment unit is determined.According toanalyzing these data, the study area is divided into three zones: the first zone ishigh incidence zone of geological disasters; the second zone is median incidencezone and the third zone is low incidence zone.(3) For information acquisition analysis of geological disasters, using theinformation acquisition model to select five evaluation indexes including terrain,rock type, fracture development degree, rainfall and mankind activities,14different states are determined as predictive variables and their values arecalculated through mathematic model of information acquisition. Then the studyarea is divided into grid units and information value of each evaluation unit is calculated. Finally the zoning boundaries,-3.75and1.875are obtained throughnatural breaks and the susceptibility degree of each assessment unit isdetermined.(4) Compared with two results from two evaluation methods, the area ofhigh-median incidence zone with using index method account for38.9%of thetotal area and among them the number of geological disasters account for90.84%of the total; while using information acquisition analysis, they are51.71%and87.25%respectively. Therefore, these two evaluation results wellreflect the susceptibility degree of geological disasters in the study area, and alsohave a better corresponding relation on the distribution of geological disasterspots, which shows that these evaluation results are more reliable. But inactually work, the evaluation reselts of information acquisition analysis whichdidn’t use AHP to determine the weight of the evaluation indexs are moreobjective and reliable. What’s more, combined with evaluation results of twomodels, zoning evaluation of three different susceptibility areas are made andsome measures on prevention and environmental protection of geologicaldisasters are provided in the thesis.