Study On The Strength And Activity Grading Of Slow Landslides In The Alpine Valley Based On SBAS

According to the landslide committee of the International Association for Engineering Geology and the Environment(IAEG),landslides have caused 14%casualties of all the natural disasters in the past 1000 years.The geological disasters in China are widely distributed and break out frequently.The direct economic loss caused by geological disasters each year took more than 20%of the total loss of natural disasters.It is difficult to confirm the location,occurring time and the scale of the geological disasters like landslides,which bring a great challenge to landslides prevention and control work.Monitoring landslides and early warning become urgent issues at present.It has an important practical significance to assessment of the state of activity and intensity of preexisting landslides for generating landslides prevention strategy.The Longnan mountainous region lies in the translational area among Qinghai-Tibet Plateau,loess Plateau and Sichuan Basin.Because of its superimposed weak belt in geological structure,stratigraphic properties,geomorphology,climate and vegetation,this region is one of the most severely landslide affected regions in China.We twelve typical river basins(267.66 km2)of Longnan as sample region and employ ground deformation velocities derived through Baseline Subsets(SBAS)technology for the assessment of the state of activity and intensity of extremely to very slow landslides.From the local government polygon landslide inventory database,there have been 450 landslides in the area.The landslides’ area is about 19.7%of the total area.We exploit SBAS data of 32 ENVISAT ASAR images of 2003-2006 and 2008-2010,combine 1:50,000 DEM data,landslides inventory data and landuse data,calculate landslides’ annual velocity,assess landslides’ intensity and activity,and analyze the result combined with the landslides’ types and land use data.There are 208 landslides and 108 landslides in the study area in 2003-2006 and 2008-2010,respectively,and their states of intensity have been assessed.We have found that landslides of which intensity are stable and extremely slow reduce 7.5 and 38.3 percentage points respectively,and landslides of which intensity are very slow grow 46.8 percentage points.So that landslides’ sates of intensity of the study area are enhanced.By assessing the states of activity of 450 landslides,we have found that 96%landslides of all that can be monitored are not stable,and all types of landslides are relatively serious.In addition,55%of the landside in intense human activity areas is active.The research results can be used to guide the local disaster management,disaster prevention and mitigation,land use and the risk management.It can also be a demonstration study for related domestic and foreign research.