A Research On Geological Disaster Risk Assessment In Shifang City Of Sichuan Province

The Shifang city belongs to Deyang City in Sichuan Province, it attached at joint of the Western Sichuan Plain and Qinghai-Tibet Plateau, which is in the South of Mian zhu, East of Mao County, North of Pengzhou City. Shifang city covers an area of 862.017km2, the total population of 43.19 million.The landscape of Shifang City shows a terrain north west to south east which is Consist of a plain,low mountains,middle mountains,alpine landforms, Shifang is located in the Longmen Mountain tectonic zone, stratigraphic occurrence changed greatly; Its region richs in groundwater and surface water, groundwater is mainly bedrock fissure water and pore water loose; human engineering activities more strongly, mainly roads and bridges, water utilities, urban construction, housing and other slope cutting. In general, the geological environment in Shifang city is complex which is designated as geological hazard prone areas in Sichuan Province.The main types of geological disast ers in the region are landslides, avalanches (unstable rock), landslides and potentially unstable slopes. According to the survey After the 5.12 Wenchuan earthquake in 2008, the city has 197 points of geological disasters, in which 71 points of landslides,16 points of unstable slopes, 79 point of collapse landslides and 6 points of debris flows. In order to identify environment background,in which the geological disasters of Shifang city after the earthquake occurred,to find out the conditions for the formation of geological disasters and the impact of factors,which determine the risk of geological disasters after the earthquake,an effective geologieal disaster risk assessment needs being ensured to prevent hazards and reduce its economic loss,a complete model for hazards assessment also must be quickly searched for,In this paper,reasonable discussions have been done into this research area,and major outcome has been obtained as follows: (1) This paper has proposed the clear geological disaster risk assessment method mentalily of Shifang city after the earthquake, also survey of field-collection of inform ation–date analysis–factor quantification–model evaluation–obtains the result–result analysis, and has completed the entire geological disaster risk appraisal system of Shifang city after the earthquake.(2) This paper anaysed the regional environment background of disasters,and spatial distribution of geological disasters ,characteristics of hazards before and after the earthquak e were compared, studied the formation of geological disasters in the conditions and influencing factors after the earthquake, and based which, select elevation, lithology, terrain slope, the intensity of earthquakes water system as the main-sensitive factors of risk assessment of geologic of Shifang city after the earthquake.(3) This paper anaysed the basic characteristics and causes of disaster of Shifang city after the earthquake, qualitatived assessment of the danger of geological disasters, and understood the characteristics of disaster of typical of Shifang city after the earthquake from a single point disaster. The results show that the major controlling factor for the formation of geological disasters is the earthquake.(4) This paper proposed the geology disaster of Shifang city after the earthquake risk appraisal's way, namely the appraisal's way was this kind of flow of analysis of characteristis of geological hazards–anysis of the causes of the mechanism–sensitive factorial analysis and the qualitative analysis inference–mathematical model super imposition analysis–quality synthetic evaluation, and has annotated this flow well with Arcview, has botatined the achievement chart finally.(5) The figure shows the results from the assessment district that , after the earthquake , geological disasters of Shifang City in high-risk area for the 123.4 7km~2, accounting for 14.03% of the total area of the city, mainly along the Yangtze River and its tributaries Shiting (such as Tongxi rivers, an unnamed tributary of Ying Hua) and between the Beichuan-Yinxiu fault; Medium risk area of 286.9 3km~2, accounting for 33.29% the total area of the city; low-risk area for the 432.27km~2, accounted for 2.68% of the total area .The results showed that after 5.12 Wenchuan earthquake, geological disasters of Shifang City in the high-risk area has increased, mainly along the Lianshan rivers and in the town of Ying Hua, west in Bajiao town and north west in Hongbai town which before the earthquake are medium risk area.