| The evaluation of susceptibility to geological disaster is am important part of evaluation of geological disaster. Geological disaster-prone zones are the areas where geological disaster can happen easily. It is very important and necessary to evaluate the susceptibility to geological disaster in order to prevent the disaster,diminish losses from natural disaster,and protect the properties and lives of the people.In this paper,the geological disasters of western area in the Himalayas which includes Gar County,Zada County,Purang County and Tarong County in Ngari prefecture of Tibet are chosen as the research subjects. Based on the field investigation and analysis of current geological disasters,combined with the current idea of regionalization of susceptibility to geological disaster , evaluation of susceptibility to geological disaster in the research area is processed. The paper has the contents listed below:General geological condition of the research area is summarized based on the collection of geological information, field investigation and analysis, and comprehensive analysis. The research area locates between the Himalayan Mountains and Gangdise Mountains in southwest Tibetan Plateau. The area has criss-cross high mountains and deep valleys, with the average latitude at least 4000m. The strata are very complex; apart from carbonic system, the strata from Presinian system to Permian system, Jurassic system as well as Tertiary system, quaternary system can all be found in this area. The precipitation in this area varies both in time and space. The surface runoff and underground water are complemented by melting water of snow on mountains.Through the grasping of geological environment, and analysis of distribution of current geological disaster, it is know that the geological disasters are distributed in group or in zone. The disaster where the latitude is between 4000m to 5500m is 89.3% of the total disasters; 34.3% disaster happened in the area where the slope is 20~35°,64.9% disaster happened in the south-faced slope,which favors the geological disaster; in terms of type of soil,59.0% disaster happened in nature meadow; during the rainy season, from June to September in every year,the disaster happens most frequently. Based on the analysis above,the basic elements that influence the disaster in the research area are the topography,geological structure, type of the soil and rock mass,and meteorology as well as vegetation.In the process of evaluation of geological disaster, it is typically important to determine the weights of every influence factor which has a directly bearing on the rationality and authenticity of the result of evaluation. In this paper, improved fuzzy analytic hierarchy process (fuzzy AHP), which is based on theory of targets decision-making and improved analytic hierarchy process (AHP), is applied to determine the weights of every factor. The advantage of this method compared to AHP is that deal with the problem of constitution validation in AHP by developing the reciprocal judgment matrix. Finally, make the weights of evaluation factors be more reasonable through several times iterating of initial ordering vector in iterating formula . The ordering vector obtained by this method is considered as the weights of evaluation factors in this evaluation of geological disaster.In this paper,a secondary fuzzy evaluation model was used in the fuzzy comprehensive evaluation. Selected 10 evaluation factors: surface elevation,slope, aspect,impact of river water from the rock group the type of impact from construction, seismic intensity, land use type, rainfall and disasters point density, constitutes the evaluation factors set. Evaluation set using four criteria, the study area, geological hazard susceptibility is divided into easy-fat, low-prone, in the prone and high-prone four. This article combines the distribution of the evaluation factors, using the "lower half ladder" distribution of the membership function. Then divided by watershed unit,unit split the mainstream line of large rivers for mesh partition boundaries. Finally,comprehensive evaluation,based on fuzzy evaluation of the maximum membership degree principle, the evaluation unit to determine the extent susceptible. Spatial analysis is performed on each evaluation factors by using GIS, thus, single-factor layers of each evaluation factors are gained. Improved fuzzy AHP is applied to calculate the weights of each evaluation factors. Then, geological disaster susceptibility of each unit is calculated by the model of susceptibility. It can be shown from the statistic of susceptibilities of units that there are jumps on 1.8, 2.1, and 2.6 on the line of the distribution curve of susceptibility. In this evaluation, the study area is divided in to high prone area(>2.6),medium prone area(2.1~2.6), low prone area(1.8~2.1) and non prone area(<1.8) by regarding the three points as the boundaries, and also is mapped. Detailed evaluations are given according to the map.In this paper, the evaluation obtained by the two models were compared, fuzzy comprehensive evaluation method of high-, medium-prone areas of the study area and accounted for 22.8% of total area, development of geological disasters in the number of accounts for the total number of geological disasters 100%; Geological Hazard Index for the high, middle-prone areas of the study area and accounted for 22.4% of total area, development of geological disasters in the number of geological disasters, accounting for 97.4% of the total. Obviously, the two evaluation results could well reflect the study area, the degree of geological disaster-prone, and the distribution of disaster-point correspondence is relatively good, that this evaluation result is reliable. Combination of two models of evaluation results, the paper on the study area in the last four levels partition the evaluation prone areas, and some advises of preventing geological disasters are given according to the result of this research. |
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