Study On Debris Flow Risk Assessment In Earthquake Area Based On Rough Set And Kernel Principal Component Analysis

Wenchuan earthquake caused a large number of secondary geological disasters such as callapses and landslides,It provided a lot of loose solid source for debris flow,at the same time,under the influence of post-earthquake effect,The shear stress of rock mass caused the rock mass structure failure and slope instability,under the condition of late rainfall,it is easy to start to provide indirect recharge for debris flow.According to the statistics,the number of debris flow after the earthquake has increased obviously compared with that before the earthquake.The geohazard chain caused by the earthquake will affect the decades after the earthquake or even longer.Therefore,it is very important to study risk assessment of the debris flow in the earthquake area.According to these characteristics of the debris flow in the quake zone,this paper takes the debris flow in the Mian-yuan River Basin of Qing ping County as the research object.Through the field investigation and the previous research data,the geological environment and development background of the debris flow are analyzed,and the geohazard chain effect is taken into account.Use statistical method and RUSLE model to estimate the dynamic reserves of debris flow.Twenty risk assessment indexes are established by means of literature survey,and the rough set is used to reduce the index.The hazard assessment of debris flow is carried out by using kernel principal component analysis(KPCA).Finally,combined with the assessment of vulnerability in debris flow area,the results of the risk assessment of the debris flow in the earthquake area are obtained.In this paper,the research ideas and methods for the risk assessment of debris flow in the earthquake area are feasible and scientific.The main achievements are:(1)Based on the history and present situation of debris flow in Qing ping County,Choose 11 debris flow area in the Mian-yuan River Basin as the research object.The meteorological hydrology,topography,lithology,geological structure and vegetation conditions of the study area are investigated in detail.The characteristics of pre-earthquake and post-earthquake are analyzed and the effects of earthquakes on the reserves and starting conditions of debris flow were found.(2)Debris flow dynamic reserves estimation model is established.Using the control variable method to identify the relationship between the single factor and dynamic reserves,and to establish multivariate nonlinear regression model,through the model to estimate the debris piled up class debris flow dynamic reserves,combined with the RUSLE model to estimate the slope surface erosion debris flow dynamic reserves to get the debris flow dynamic reserves.(3)Combining previous research of debris flow risk assessment and field investigation results of the study area,debris flow influence factors are checked.And for attribute reduction to the primary evaluation index according to rough set theory by taking the discernibility matrix.Finally the debris flow hazard evaluation index system are established.(4)To introduced the kernel function and kernel principal component analysis.After standardizing original data of the ditch,using KPCA to extract the optimal principal component.Through the calculation of principal components to get the hazard assessment results of ditch in the study area.(5)On the basis of the geological disaster risk evaluation theory,the technique of vulnerability assessment in Debris flow risk assessment is discussed.The influencing factors of the vulnerability of debris flow,that is,the possibility of being damaged,the degree of damage and the value of Hazard-affected Bodies,are considered.The method of evaluating the vulnerability of single debris flow in mountain area was established.Combining with the debris flow hazard evaluation and achieve risk assessment.