Application Of Newmark Models For Risk Assessment Of Regional Earthquake-induced Landslides

As one of the common earthquake secondary disasters,earthquake-induced landslide often causes serious economic and property losses and casualties and becomes a tricky problem in many mountainous and earthquake-prone countries.Mapping the susceptibility and establishing the regional risk zoning map is an effective way to reduce the seismic landslides disaster.In this paper,taking Ganzi Tibetan Autonomous Prefecture of Sichuan Province,China as the research area,based on the simplified Newmark model,we mapped the seismic landslide risk assessment.Meanwhile,we analyzed the main factors that control the accuracy of the Newmark model,and introduced the improvement methods of the obtaination of rock mechanical parameters as well as the influence of river erosion.(1)In the whole region,based on the topographic slope and geological lithology data and using the Newmark model,we calculated the critical acceleration and obtained the seismic landslide susceptibility map in the Ganzi area.Furthermore,the risk assessment of the seismic landslide in the Ganzi area are mapped under different ground shaking conditions,respectively in the 50-year exceedance probability of 63%,10%,and 2%,100-year exceedance probability of 1%,and different ground motion intensity of 0.1g ～ 1.0g.The results show that the eastern,southern,and western parts of the Ganzi Prefecture are highly sensitive to landsliding.This result is consistent with the actual distribution of the field landslides,indicating the reliability of the landslide sensitivity maps.As a whole,with the increase of earthquake intensity,the degree of landslide risk increases.The high landslide risk areas are mainly in the southeast and northwest structural zones and their vicinity of the study area,mostly along the river system and structural belts;the moderate risk areas are mainly located in low mountainous areas,middle mountain and hilly areas;the low risk areas are prone to the central hilly areas and high altitude areas.(2)The development of active faults creates favorable conditions for geological disasters and directly affects the distribution of the landslides.The Luhuo section of the Xianshuihe fault and the Ganzi section of the Ganzi-Yushu fault with high degree of research and strong seismic activity are selected to evaluate the effects of the active faults on the hazard of seismic disasters.According to the hazard maps,the high-risk areas are concentrated near the fault zone,and the overall trend of hazard risk decreases with the increase of the distance to the fault,indicating that the seismogenic fault has a great influence on the occurrence of seismic landslides,which provides a reference for the further study of seismic landslide hazard evaluation methods.(3)For the small regional scale,the landslide risk assessment in the Kangding City is analyzed.Based on the slope and lithology data of the Kangding study area,the landslide risk assessment is carried out based on the peak acceleration of 50-year exceeding probability of 10% ground motion in the Kangding area and the horizontal ground shaking motion of the Moxi and Selahe faults.The results show that the high landslide risk areas mainly concentrate close to the Moxi fault with higher ground motion potiention comparing to the landslides distributed around the Selaha fault.The landslide susceptibility distribution is similar to the risk zoning of the whole Ganzi area,both indicating that the ground shaking controls the slope stability.The comparison of the research results with the actual landslide distribution obtained by remote sensing images further indicates the effectiveness of the Newmark model in earthquake-induced landslide prediction.(4)The slope stability under seismic conditions is closely related to the slope material composition.The rationality of the input rock mechanical parameters decides the calculation results of the Newmark model.So far,the rock mechanical parameters are given subjectively and do not consider the spatial and temporal variation of rock mechanical parameters in a large area.In order to make the lithologic parameters more reasonable,we assigned the rock mechanical parameters by considering the slope degrees in each lithology group and recalculated the seismic landslide sensitivity distribution in the study area.The AUC value of the ROC curve of the sensitivity distribution using the improved method are larger,indicating that the improved landslide sensitivity result is more reliable.(5)The erosion aggravate the geological disasters on both sides of rivers.Therefore,the relationships between fluvial geomorphic parameters and landslides will further the understanding the of the formation mechanism of the landslides.Taking the upper reaches of the Jinsha River in Ganzi Prefecture as the study area,we calculated the river steepness coefficient in the upper reaches and analyzed the relationships between the landslides on both sides of Jinsha River.The results show that the higher values of the steepness index in the upper reaches of the Jinsha River are concentrated in the intersection of the main stream and tributaries of the Jinsha River,and the steepness index value is larger in the areas where landslides contrated.At the same time,there is a mutual influence between the river steepness index and the distribution of landslides.The erosion datum plane of the upstream reaches where landslide occurs will be elevated,resulting in the decrease of the erosion rate and river steepness index of the upstream.