| Strong earthquakes in the mountains areas often induce massive geological hazards,causing a lot of loose debris in the slope and channel.These deposits are highly prone to sliding again in the following years,triggered by rainfalls,and provide the source materials for the debris flow,caused by geological hazards after an earthquake occurred more frequently than before the earthquake increased significantly,also threat post-disaster reconstruction and disaster area people's life and property safety.In 2008,the "5.12" wenchuan earthquake Ms8.0 triggered nearly200,000 earthquake landslides,which is the largest single earthquake-induced landslide in the world.The earthquake caused the geological environment of mountainous areas to be fragile,and a large number of loose material sources,resulting the disaster and the disaster chain effect is obvious in the post-earthquake ten years.For example,"9.24" in 2008 and "8.13" in 2010 caused a mass debris flow events,which greatly exceeded the original expectations.The lack of understanding of the dynamic evolution mechanism of post-earthquake geological hazards has severely restricted the reconstruction and economic development of the disaster areas.How does geological hazards evolve in time and space after earthquake? How long will the post-earthquake effect last? What are the rules of material movemnet after earthquake?These are the scientific problems that need to be solved,and it is also of great significance to guide earthquake disaster prevention and mitigation.Therefore,we selects 42 catchments near the epicenter,where is at yingxiu-wenchuan along the minjiang river basin,as the main research area.Based on the multi-temporal high-resolution remote sensing images,using the method of artificial visual interpretation combining field review,set up one of the most complete database of geological disasters after an earthquake.Based on this database,the frequency and spatial distribution of geological hazards in the post-earthquake disaster are analyzed,and the influencing factors of controlling its evolution are preliminarily discussed.Through different scales,the regional scale and basin scale have studied the evolution rules of material transport over time and space.Study on material movemnet in regional scale main estimate and analysis with earthquake landslide deposits,and which has been transported to the channel after the earthquake,or been carried from the mountain area by debris flow,to quantify the earthquake effect,and provide quantitative indicators of mountainous landform evolution after the earthquake.Study on material movement in basin scale,through many remote sensing image,DEM and geophysical survey(ERT),main rebuild the formation of beichuan river basin of the debris flow events for many times,and the quantitative analysis of material motion characteristics and mass wasting.The main research results show that: After the earthquake,the earthquake disaster was greatly increased,especially in the first two years after the earthquake,a large number of earthquakes occurred in the wake of the earthquake,and resulted in massive debris flows.And then as time goes on,the slope body repair itself(increased of consolidation degree,reduced of permeability,loss of fine particulate matter,etc.),vegetation cover,a reduction in the effective source materials and other factors,make the landslide and debris flow quantity showed a trend of obvious attenuation(from2008 in 9189 to 2015 in 221).The scale of the landslide is also a key factor in controlling its activity,and the study found that the active period of large-scale landslide is longer.From the perspective of space evolution,post-earthquake landslide is more prone to occur in relatively high altitude area,but over time,it is gradually shifted to low elevation.At the same time,the larger the drainage area is,the more likely it is to be activity(or slide again).Through regional scale and the basin scale mass wasting quantitative analysis found that a large number of(regional scale 99.3%,basin scale 95%)coseismic deposits remained in the mountain valley,of which only small part(10% regional scale,basin scale 21.78%)transported to the downstream channel by movements.Analysis of the characteristics of sediment transport of yangjiagou in beichuan county shows that,the integration of ERT electrical survey and multi-remote sensing image is effective for the reconstruction of historical material movement of historical debris flow events,to a certain extent,make up for the lack of terrain data,and calibrate its error,improve athe ccuracy and reliability of channel debris survey results.In addition,also found deposits of landslide dam is obvious to carrying to channel in the form of slope debris flow(erosion)after the earthquake,and the material transport in the channel is mainly controlled by different gully form and topograpgic factors.The overall trend of post-earthquake material transport and the number of activity post-earthquake geological disasters are consistent with the same attenuation trend,which has basically recovered to the pre-earthquake level.Therefore,according to the coseismic earthquake landslide volume,erosion rate and the earthquake recurrence interval to estimate,find that before the next magnitude 8 earthquake happened,longmenshan area are still have a lot of coseismic materials produced by the wenchuan earthquake landslide staying in the mountains,cannot be fully carry away,which can have long-term impact on the mountainous landform evolution. |
PDF Full Text Request