| Lanzhou, located in the west of the Loess Plateau, is a typical city of mountain valley in terrace of the Yellow River. Special terrain, landform, geology and climatic conditions and strong human activities cause frequent geological disasters, like landslide, collapse, debris flow and ground collapse, which makes Lanzhou become the one of the cities having most serious geological disasters and one of the four cities having the serious geological disasters following Kalan, Guatemala and Alma-Ata in Kazakhstan. Quick urbanization, unreasonable agricultural production and engineering construction as well as the increasing extreme weather in the context of climatic changing make the geological disasters more and more serious, the most severe of which is surface deformation including landslide, collapse and unstable slope.Recently, interferometric Synthetic Aperture Radar has developed quickly, which makes Mm level monitoring for the surface deformation become possible. At the same time, this kind of technology is widespread, frequent and quick. It can cover hundreds and thousands land, adaptable to wide scale monitoring. Applying interferometric Synthetic Aperture Radar in monitoring geological disasters has become one of the hottest topics in the field of geological disasters. It can get rid of the traditional GPS leveling, and we can receive longtime graded data. It can also provide us with effective geological disasters monitoring, warning and danger evaluation. The quick development of interferometric Synthetic Aperture Radar offer technological support for highly accurate and quick monitoring technological disasters in large scale.In this thesis,41 Envisat ASAR images were captured and detected surface deformation using PS-InSAR in study area. Based the results of surface deformation, the spatial distribution of surface deformation and slope hazards were compared and analyzed. And then, we choose AHP model to analyze slope hazards susceptibility in study area. We compared the regions which have high susceptibility with the regions which have the high surface deformation velocity. The result shows the two regions almost consistent. We compared high susceptibility region that have the high surface deformation velocity.The following three main research results were obtained:(1) In the period extending from 2003 to 2010, the deformation velocity in Lanzhou city is found to being between -6.8mm/year to 5.0mm/year. The velocity of main city is found to being between -2mm/year to 2mm/year. The flood plain and Class I terrace of the Yellow River are stable. The unstable regions distribute on the region which near the slope around the city and above Class III terrace of the Yellow River. In our field work, we investigate and analyze the cause of the high unstable regions which the velocity is more than ±4mm/year. Based the results of PS-InSAR, we research the occurred geohazards and the potential geohazards in these regions. In the high unstable regions, the geohazards were classified. The results that there are three types slope hazard:landslides, collapse and unstable slope. The main reason of the cause of unstable regions is human activity.(2) Based on the data of surface deformation and slope hazards, we study the distribution and the cause of surface deformation and slope hazards in different impact factors. We get the three types of slope hazards:landslides, collapse and unstable slope. In study area, the surface deformation in different impact factors mainly distribute on 0°～5° and 5°～10° slope degree, suddenly increase in the ranges of 25°～30°; N aspect; 1486m～1686m altitude, suddenly increase in 1986m; clay, sandy soil and loess on lithology; settled area on land-use; 0～0.2 NDVI. In our deeply research, the mainly causes of surface deformation are lithology and human activity. the slope hazards in different impact factors mainly distribute on 20°～25° and 45°～50° slope degree; S and SW aspect; 1486m-1686m altitude, suddenly increase in 1986m; clay, sandy soil, loess, sandstone and shale on lithology; settled area on land-use; 0-0.2 NDVI. The same to the surface deformation, the mainly causes of slope hazards are lithology and human activity. The comparison between the density of surface deformation and slope hazards reveal the distribution of surface deformation and slope hazards either consistent or inconformity. And then, we deeply analyze the cause of inconformity. Based on these methods, we can use PS-InSAR to detect surface deformation in study area and use the results with the features of distribution of slope hazards to identify, monitor the potential slope hazards in study area. It reaches the hazards prevention and mitigation of slope hazards in a large scale by the purpose of the new technology.(3)In order to verify the effectiveness of the PS-InSAR direct detection techniques to identify the unstable region and get a more reliable evaluation result of study area, we choose AHP model to assess slope hazards susceptibility in study area. Using AHP model can better take into the experience of experts. Based AHP model, we get lithology is the most important impact factor of controlling slope hazards. Meanwhile, the slope hazards susceptibility results from AHP model with many impact factors are consistent with the results from PS-InSAR detected high surface deformation. It is proved that the PS-InSAR technology can quickly, accurately to identify slope hazard in large scale and analyze sensitivity directly. It can be applied to identify slope hazards in large scale and analyze slope hazards susceptibility. |
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