Study On Loess Landslide By Strong Earthquake Hazard Risk Assessmengt In High Intensity Earthquake Mountainous Areas

In loess plateau, the terrain is very complicated, the geological structure is complex, the faults are developed, and the strong earthquakes occur frequently, which makes the loess landslide become one of the most serious geological disasters in the loess area. On the 16 th of December, 1920, an earthquake of magnitude 8.5 on the Riehter scale occurred in Haiyuan Country is one of the biggest earthquake in the history of our country. Loess landslide induced by the earthquake are mainly distributed in the Liupan Mountains to the west, Haiyuan earthquake meizoseismal region IX- X in Xiji, Haiyuan, Guyuan County. Haiyuan earthquake has a very significant characteristics: along the earthquake fault zone within the scope, the earthquake induced landslide destruction of the most serious area not in the X- XII region, but in the IX- X of Xiji County in southwest.Taking the Hulu river and Lanni river in Xiji County as research object,based on the analysis of field investigation data and geological data in the study area,using the basic theory of digital elevation model(DEM), GIS and quantification method study on loess landslide hazard assessment, and quantitative risk assessment on the typical single Dang Jia cha landslide. The main achievements were made as follows:(1) Based on existing research data collection and field investigation, from the morphological features of the landslide, boundary characteristics, motion characteristics, failure types, summary and analysis the different characteristics between the loess landslide inducing by strong earthquake and under the normal gravity environment.(2) Based on the DEM of the study area, using ArcGIS spatial analysis function to extract the landslide basic data and analysising the law between loess landslide distribution and slope, slope direction, formation lithology(loess thickness), terrain prominency, distance from drainage, distance from the seismogenic fault. we can come to conclusions as below:(1)Earthquake slope is concentrated in 5 degrees to 25 degrees, accounting for 72% of the total number of landslides in the study area;(2)Earthquake landslide slope mainly concentrated in the northeast(60 degrees to 90degrees) and southwest(260 degrees to 290 degrees), accounting for 42% of the landslide in the research area;(3) The loess thickness of the landslide is mainly concentrated in the range of 25 m ~ 35 m, accounting for 72% of the total number of landslides in the study area;(4) The terrain prominency of the landslide is mainly concentrated in the range of 40 m ~ 60 m, accounting for 39% of the landslide in the research area;(5) The distance from the earthquake induced landslide is mainly concentrated in the range of 35 ~ 55 km, and there is no more distance from the fault,the smaller the number and density of the distribution of the geological hazards.Finally, analysis the reason of loess landslide dense development in the study area from fault structure, formation lithology and topography and landform.(3) Through research of loess landslide characteristics of the study area and distribution. The selection of slope, slope direction, formation lithology(loess thickness), terrain prominency, distance from drainage, distance from the seismogenic fault as the evaluation index, using quantitative theory establishment of loess landslide risk evaluation model, based on ArcGIS software to complete the landslide risk assessment, research area earthquake landslide danger division for four grades:high risk areas(2.34-3.32), dangerous area(1.95-2.34), low risk area(1.54-1.95), very low risk area(1-1.54).(4) Quantitative risk assessment for the Dang Jia cha landslide. Based on Monte Carlo method, the probability of failure of the stability of the landslide is calculated,which is 60.89%, which is a high risk. The discrete element software is used to simulate the motion process of the landslide under earthquake action, and to determine the influence range of the landslide. Make an analysis for vulnerability of element at risk within potential hazard range of the Dang Jia cha landslide,getting the hazard-affected probability and loss rate of element at risk, and calculating the value loss of people's life and property value. Based on the single landslide risk calculation formula, the Dang Jia cha landslide population total risk that value for86.32 and economic loss risk value reached 145.068, and Dang Jia cha landslide risk value and landslide acceptable risk level are compared, it is not acceptable risk level.