Research On Survey Of Earthquake Triggering Geohazards And Risk Assessiment In Wenchuan Earthquake Stricken Areas Using RS And GIS

"5.12"Wenchuan earthquake triggered a series of collapses, landslides, debris flows, and other geohazards, which thus resulted in great damage to people's life and property. The study area situated in the north of longmenshan fault zone belongs administratively to the Qingchuan County of Sichuan province,which is one of the worst-hit mountainous areas in whenchuan earthquake. Qingchuan Country often scathed by earthquake in history , because of its particular location , it is about 100km away from Qingping , Songpan , Maowhen , Pingwu ,and other high intensity areas. In wenchuan earthquake ,three of the aftershocks exceeded magnitude 6 , including the maximum aftershock with magnitude 6.4 occured in the study area at 4:21 p.m on May 25 , 2008.With the complex geological structure and plenty of geological hazards , the study area's geological environment will be more brittle after 5.12 Wenchuan earthquake , thus easily lead to more hazards in the conditions of heavy rainfall. therefore, to strengthen disaster prevention and the research work of earthquake—triggered geohazards have great significance.This paper took the earthquake-triggered geohazards in Qingchuan County after "5.12" earthquake as the research object, by the use of field investigation in Qingchuan County and remote sensing interpretation data for typical areas , this paper researched the development features and distribution rules of the earthquake-triggered geohazards, and made analysis and evaluations for geohazard risk for Qingchuan County after the earthquake by the use of GIS spatial analysis methods , this paper has gained the following conclusions:(1) Aerial remote sensing images have the characteristics of access to fast, high resolution, compared to traditional ground surveys, which have a strong capability of the macro grasp , could conduct in-depth investigation and detailed analysis for the elements of disaster body , which is highly effective. This paper used a method which make a combination of the plane-like interpretation and punctate-like interpretation, made interpretation respectively for the three main of geohazard : landslides, collapse and debris flows, from the results of the interpretation, the number of collapses and landslides in the main distribution, landslides slightly larger than the collapse in the area, the two were closer. (2) The earthquake-triggered geohazard had marked seismic fracrure effects, topography effects, aspect effects, disaster-chain effects, and also have high density characteristics.. Earthquake-triggered landslide is generally located in the middle and the upper body of the slope, the trailing edge after always developed from the peak or the watershed edge of a hill, the development position was relatively high; earthquake-triggered landslides and collapses were always with the characteristics of high-speed & far-slip, and the characteristics of regional distribution; earthquake-triggered debris flow had the characteristics of rich source ,controlled by the fault and the small basins, the occurrence of which was lagged with time. (3) The fault, lithology, drainage, slope and elevation had a control role effect for the disaster development ,and had a higher sensitivity, this paper using GIS made sensitivity analysis for the geohazard on the study area by five impact factors: terrain and slope, elevation above sea level, away from the active fault distance, formation lithology and water ,on this basis of which, this paper made the use of AHP to determine the weights of each factor and to establish risk assessment model, and finally made the overlay analysis by the use of spatial analysis functions of GIS, and produced the geohazard risk assessment maps for the study area. The division of geohazard risk results was corresponds to the distribution of the geohazard density of points , The results of the study reflects the distribution rules of geohazard triggered by the earthquake for the study area, which was in line with the accuracy of regional evaluation, but also illustrated the reliability of indicators adoptived in the evaluation system and factor. Based on the development features of the earthquake-triggered geohazard and geohazard risk assessment for the study area ,this paper provide the measures and recommendations for the work of geohazard prevention and mitigation.