Study On Seismic Landslide Hazard Assessment In Wenchuan Earthquake Severly Afflicted Area

Seismic landslides hazard assessment is one of the key issues in landslide risk assessment framework. This thesis takes Wenchuan Ms 8.0 earthquake severely afflicted 11 counties as study area. Emergency response rapid assessment of landslides triggered by intensive earthquake and post-earthquake hazard assessment of due to future rainfall and potential earthquake is researched; main progresses and resulrts is achieved as following:1. Seismic landslide hazard assessment model based on simplified Newmark cumulative displacement is preliminarily developed and improved using Arcgis spatial analysis modeling function, the method of seismic landslide loss rapid assessment is provided. With the real-time earthquake ground motion parameters of Wenchuan earthquake, empirical engineering geology lithology formations, topographic slope data, rapid back analysis assessment of landslide hazard and the loss due to Wenchuan earthquake is carried out; the results provide scientific and technological support for emergency response dicision-making.2. Spatial distribution of seismic landslides triggered by Wenchuan earthquake is significantly affected by Longmenshan fracture zone, topography and stream valleys. The seismic geohazards mainly consist of collapses, landslides, debris flows, debris slide (s) and debris-avalanches, followed by sandy soil liquefaction and ground subsidence. The former 3 geohazard types and debris-avalanches usually cause more damage, and debris flow (s) distribute most widely. In the post-earthquake reconstruction, lots of loose structural rock & soil mass and landslide debris deposits located in slope surface and valley banks can be easily carried by heavy rainfall or river flow to transform into debris flows, to become the most threatening geohazard type. This evolutionary process indicates the post-earthquake lag and chain characters of seismic landslides.3. Taking Wenjiagou seismic debris-avalanche for case study, the inducing context, ground motion triggering mechanism, spatial characteristics and evolution process of high-speed and long runout of debris-avalanche are analyzed. It is indicated that widely spread debris-avalanches triggered by Wenchuan earthquake do not only cause lots of damage, but also be easy to transform into new debris flows due to rainfall, which should be paid more attention to in reconstruction after the earthquake. At the same time, this case study provides reference for investigation and hazard assessment of major hidden landslides in potential intensive earthquake zone similar to Longmenshan structural zone.4. With 2.5m-resolution SPOT5 remote sensing image of Shikanhe river basin shot immediately after the earthquake, rapid identification and extraction methods of seismic landslide based on image classification techniques are comparatively analyzed. With the method of composing object-oriented feature extraction and artificial interpretation, seismic landslides in Shikanhe river, Jianjiang river, Mianyuanhe river and Minjiang river basins is accurately interpreted. The seismic landslide intensity levels of typical river basins and whole study area is assessed using area and point density respectively.5. Results of seismic landslides susceptibility, hazard and loss rapid invesion assessment in Wenchuan earthquake with simplified Newmark model show that Yingxiu township, Beichuan county, and Nanba township etc. locate in heavy loss zone, Qingchuan county lies in transition zone from heavy to moderate loss zone, Pingwu county and Diexi township lie in light loss zone; these results are well validated in field investigation.6. Post-earthquake landslide susceptibility is assessed using information model; the result indicates regional distribution of potential landslides and substance source for debris-flows. The daily maximum rainfall value with 90%'s cumulative probability density (10% probability of exceedance) in 2 years is predicted using Weibull probability density function model; then the landslide hazard assessment due to future rainfall is carried out with the safety factor Fs calculation. Consequently, the landslide hazard assessment due to potential earthquake with 10% probability of exceedance in 50 years is assessed with the improved Newmark displacement model; the result shows that highly landslide hazard zone mainly locate in landslide clustering area controlled by the seismic faults, and provides valuable guidance for reconstruction in Wenchuan earthquake severly afflicted area and hazard mitigation and prevention.This thesis is supported by 973 Project subject "Study on risk management system of major secondary landslides triggered by Wenchuan earthquake" and 11th 5-year Science and Technology Support program "Study on monitoring & warning of major landslides and key technology of emergency response".