Risk Assessment Of Earthquake-induced Collapse Disaster In Jiuzhaigou Scenic Area

On August 8,2017,an Ms7.0 earthquake(33.20°N,103.82°E)broke out in Jiuzhaigou County,Aba Prefecture,Sichuan Province,with a focal depth of 20 km.The epicenter was located in Biman Village,Yuzha Town,Jiuzhaigou County,and only the core scenic spot of Jiuzhaigou.5 km.Affected by the earthquake damage to the rock mass,the core scenic spot of Jiuzhaigou has produced a large number of hidden danger points of high or high level,which seriously threatens the safety of life and property of visiting tourists and local residents in the core scenic spot of Jiuzhaigou.In view of this,this study takes the "8.8" Jiuzhaigou earthquake core scenic spot collapse geological disaster as the research object,through the detailed investigation of multiple means on site and the refinement of a large number of related literatures,analyzes the development and distribution of coseismic induced collapse disasters in the core scenic area of Jiuzhaigou.And the influencing factors.On this basis,this study carried out multi-scale risk assessment of the earthquake-induced collapse disaster in the core scenic spot of Jiuzhaigou from the risk assessment of collapse of typical slopes to the risk assessment of regional collapse disasters in the core scenic spots of Jiuzhaigou.The evaluation results are highly consistent and consistent with the actual situation,and have a strong guiding significance for the post-disaster reconstruction work in the core scenic spot of Jiuzhaigou.The main research results include the following aspects:(1)Combined with remote sensing images,aerial photography of drones and detailed methods in the field,the investigation and analysis of the collapse disasters in the core scenic spots of Jiuzhaigou were carried out.The results show that the collapse disasters in the core scenic spots of Jiuzhaigou are mainly distributed in the mountains along the Rizhigou and Shuzhenggou in the scenic spot.The relative elevations are in the range of 0-100 m,200-400 m and 600-700 m,accounting for the total number of co-seismic collapses.59.04%.It can be seen that there are a large number of high-level and extremely high-level collapses in the core scenic spot of Jiuzhaigou,which poses a great threat to post-earthquake reconstruction and risk management.(2)The collapse disasters still existing after the earthquake are roughly classified into the following two categories according to the identifiability of the signs of deformation: 1)hidden danger points of collapse disasters with obvious signs of deformation;2)regional geological bodies without obvious deformation or difficulty in identifying deformation.Through statistical analysis of the developmental characteristics of typical earthquake-induced collapse disasters,it is found that the elevation and slope of the typical collapse disaster and the collapse source induced by the “8.8” earthquake;the distance from the earthquake fault;the density of the regional small structure,and There are dominant development intervals in the distance of the water system.(3)Based on the high-precision DEM data,based on the ArcGIS geographic information platform,based on the 3D terrain modeling and Rockfall analyst numerical simulation software,the sensitivity of the motion parameters of the collapsed stone in the real 3D terrain model was studied.For the evaluation index collapse rock energy and lateral motion range-discrete,the normal recovery coefficient,tangential recovery coefficient,initial horizontal velocity,mass M sensitivity is greater,for the evaluation index collapse rock stone bounce height,In terms of running speed and moving distance,the normal recovery coefficient,the tangential recovery coefficient,the initial horizontal speed,and the mass M are more sensitive.Therefore,the normal recovery coefficient of the slope table,the tangential recovery coefficient,the initial horizontal velocity of the caving stone of the caving block and the mass M are the main factors to be considered in the risk assessment of collapse disaster management.(4)Considering that the threat degree of collapse of a typical slope is the most pressing problem facing the post-disaster reconstruction and collapse risk management in the core scenic spot of Jiuzhaigou,it starts from the failure of the collapse of the block rock to the accumulation of motion,for the typical slope Risk assessment of collapse disasters.Among them,there are 40 typical collapse disasters with low risk level,accounting for 37.38% of the total,30 typical collapse disaster points with medium risk level,accounting for 28% of the total,and 28 typical collapse disaster points with high risk level.It accounts for 26% of the total,and there are 9 collapse points at very high risk levels,accounting for 8.4% of the total.It can be seen that the typical slope collapse disasters identified in the core scenic spots of Jiuzhaigou are medium and low risk grades,while the typical slope collapse disasters with high risk and very high risk grades mainly exist in the residential areas and core landscapes within the scenic spots.Tourist center and other population gathering areas.Therefore,it is recommended to conduct disaster management and regular inspections on the typical collapse points of medium,high and very high risk levels to avoid damage to scenic spots and prevent losses caused by collapses.(5)Based on the results and analysis of the field survey,nine evaluation index factors were selected as the basic evaluation indicators,and the evaluation factors collinearity diagnosis and significant diagnosis were finally used to determine the eight evaluation index factors to jointly construct the risk assessment system of Jiuzhaigou core scenic spot.The binary logistic regression model and the information method are used to evaluate the regional risk of Jiuzhaigou core scenic spot.Among them,high-risk areas and extremely high-risk areas are mainly distributed in the upper middle part of the left bank of Shuzhenggou,the upper part of the mountain on the right bank of Jinghai,the mountain on both sides of Danzugou and the mountain on both sides of the Pandahai-Rizilgou protection station.These areas are subject to obvious local structural control,the rock mass is relatively fragmented,and it is also in the extreme earthquake area of the “8.8” earthquake,which is basically consistent with the field investigation results.(6)The regional risk assessment model and the vulnerability assessment model are combined to obtain the regional risk assessment model of the study area.According to the results of risk assessment,the high-risk areas and extremely high-risk areas in the core scenic spots of Jiuzhaigou are mainly concentrated along the mountainsides of the Shuzhenggou-Jinghai-Wuhuahai-Rizilgou protection station,and the dangerous high Dan Due to less human activities and less vulnerability assessment,the final risk assessment results are relatively low.