Distribution characteristics and influence factors of land subsidence in Beijing area

Land subsidence is one of the main geological disasters in Beijing area. In this study, the authors investigated the spatial distribution characteristics of land subsidence in Beijing area by using the permanent scatter interferometric synthetic aperture radar (PS-InSAR) technique and studied the relationship between the multiple factors of land subsidence and the deformation obtained by PS-InSAR on the GIS spatial analysis platform, . Some conclusions have been reached:(1) The land subsidence in Beijing area mainly occurs in the east, north and south of the plain, where there are multiple settlement centers, with the maximum settlement rate reaching 152mm/a. The regional uneven subsidence areas are obvious, and there is a trend that these areas are connected with each other to form a complete subsidence region. (2) The distribution of land subsidence areas is controlled by structures; the subsidence area is mainly located in the area of the sedimentary depression formed by several major active faults, which is in agreement with features of the Quaternary deposit. There is an obvious corresponding relationship between the development trend of the land subsidence and the strike of active faults. In the area of active faults, the land subsidence section line shows obvious turning or abrupt change, and the uneven subsidence on the two sides of the fault is very obvious. The layered settlement is directly proportional to the cohesive soil in the corresponding layer. The spatial distribution of the land subsidence has a good agreement with the stratigraphic structure and the thickness of the compressible cohesive soil layers in Beijing area. The range of the land subsidence area expands from the northwest characterized by the single structural zones to the southeast characterized by the multistructure zones. The areas where the settlement rate is more than 50 mm/a are mostly distributed in the area whose thickness of the compressible cohesive soil layers is more than 100 m. The settlement centers are in good agreement with the large thickness of the cohesive soil layers. (4) The second confined groundwater (top and bottom depth being 100~180 m) exploitation is the most influential factor responsible for the land subsidence, and the settlement centers are in agreement with the groundwater funnel.