Landslides Hazards Assessment In Qin’an County,Gansu Province

The Qin’an County is located at the north of Tianshui City,southeast of Gansu Province. The fragile environment results in frequent landslides and poses a great threat to the whole county’safety. From the geological data collection and field investigation of this area, this thesis makes the investigation projects of geological disaster in Tianshui City and establishes landslides database of whole county. BY the combination of the AHP model with GIS software, this thesis makes susceptibility area and dangerous area’s zonation in this county. With these studies, the main progress and conclusion of this thesis are obtained as follows:1) Background of the formation of the landslides in Qin’an County.Qin’an County is placed in the QiLian folded tectogene, which is in the composite area of many sets of structure. The complicated tectonic pattern, the diverse strata and the rock property, the intense and frequent earthquake activities, the active geotectonic movement, there are many rivers, which corrode the bank intensity. The degree of vegetation cover is low. The nature environment has been effected by human activities. The combined actors provide a good environment for the development of the landslides in Qin’an County.2) The distribution rule of the landslides in Qin’an County.Landslides are the main types of geohazards in Qin’an County. The landslides presents is mostly in the first or second bayous of HuLu river.3) The major controlling factors and inducing factors of the landslides in Qin’an County.The major controlling factors of landslides of this county are landforms and topography through the analysis of landslides database about the whole county, that is, slope structure, the degree of cover vegetable, the status and rock property, hydrology, river system geological structure etc. The main inducing factors are continuous rain, the heavy rainstorm and earthquake.4) Through the AHP model and GIS software, this thesis makes zonation of landslides hazard susceptibility area and dangerous area in Qin’an County.Through a analysis of the distribution features and main factors of the landslides, we can filter out the major factors of susceptibility evaluation and use the AHP model give weight of these factors. Based on the ArcGIS, this thesis do statistic analyze and assign values, build up the index model of susceptibility. We estimate the values of each factor by GIS softare on computer, and make zonation of susceptibility. Based on this, we get the induce factor of rainfall and earthquake, and obtain the danger zonation of landslides of whole Qin’an County.By calculation, the hazard dangerous area of this county is divided into four levels, that is, high, medium, low and lowest. The corresponding areas are 353km2,559.9 km2,438.03km2,253.19km2. The hazard point density is 39.07/100km2,25.04/100 km2,15.29/100 km2, 9.08/km2.