Spatial-temporal Evolution And Susceptibility Assessment Of Post-earthquake Landslide Of The Wenchuan Earthquake

The devastating 2008 Wenchuan earthquake with a magnitude of Mw 7.9 was the largest seismic event in China.It was devastating not only due to triggering unprecedented amount of co-seismic landslides,but also a series of post-earthquake geo-hazards.For example,the intense rainfall on 24^th September 2008 initiated widespread debris flow in Beichuan County,which damaged many roads and caused42 fatalities;the catastrophic and clustered debris flows induced by rainstorm from 12to 14 of August,which destroyed reconstruction buildings.Also the reactive Tangjiawan landslide dammed the Duba River.All of these unpredictable post-earthquake geo-hazards highlighted the importance of Spatial-temporal evolution of post-earthquake landslide.And it is obvious that the susceptibility assessment according to the understanding of evolution of post-earthquake landslide would be helpful for mitigation.Here we select 42 catchments near the epicenter and the main fault as the study area,which covers 463 km².Based on a large amount of pre-and post-earthquake satellite images,we established a detailed landslide mapping method and prodeced a multi-temporal polygon-based inventory.The inventory was made up with 210pre-earthquake landslides,9189 co-seismic landslides and 7422 post-earthquake landslides.The mapping inventory as data source,we quantify changes of active area,size frequency and types of movement.The result shows that the total area of pre-seismic landslides is small,while the co-seismic area is 120 times of pre-seismic landslides.In the following years the active area decreased,it was only slightly larger than pre-seismic area until 2015.According to the total area of active landslides and size-frequency distribution,we think the rate of landslides return to pre-earthquake level within 7 years.Besides comparing the co-seismic area that sufferd post-seismic reactivation,we find that the size of the still-active co-seismic area increased over time.It means that the large landslide were more susceptible to reactive than small one.This study presents the GIS-based statistical models of post-seismic landslide susceptibility mapping for each types of movement.Firstly,a logistic regression and information value model were used to produce susceptibility map for the reactived co-seismic landslides.Five factors including average depth of deposit,elevation,slope,aspect,distance to river were selectd as controlling factors.The relationship between the reactived landslide and factors were identified by stastical model.We established a new validation method that use the inventory of 2013,2015 to validate the susceptibility molde,which shows the true predict rate were 73.99%?78.95%respectively.Secondly,the more reasonable logistic model,considering PGA,distance to fault,elevation,slope,aspect,distance to river and lithology,was adopted for post-seismic new landslide.Finally,the analytical hierarchy process(AHP)based debris flow susceptibility model combined with the mapping results of reactives landslide and new landslide was produced.