Permanent Scatterer investigation of land subsidence in Greater Cairo, Egypt

Abstract

SUMMARY Land subsidence is a major geomorphic problem commonly associated with densely populated areas, such as the Greater Cairo area. Prior to this study, rates and patterns of land subsidence in Greater Cairo were not known. The Permanent Scatterer interferometric approach has been applied in this study to detect and measure the magnitude and the spatial and temporal variations of subsidence in Greater Cairo. Thirty-four Interferometric Synthetic Aperture Radar (InSAR) images acquired by the European Radar Satellites (ERS-1 and ERS-2) during 1993–2000 have been used in this investigation. The main contributing factors to the rate of land subsidence in Greater Cairo include natural sediment compaction, tectonic activity and groundwater pumping. However, the measured rate of land subsidence is found significantly impacted by anthropogenic factors rather than natural factors. The average measured rate of subsidence is approximately 7 mm yr −1 during the period of observation, and the spatial and temporal patterns of land subsidence are demonstrated by a time-series of surface deformation maps. InSAR results show differential surface displacements along the major surface and subsurface faults and indicate pumping-induced subsidence, which is characterized by bowl shapes, in districts of high population density. The detected pattern of land subsidence in Greater Cairo implies a considerable contribution from the subway network as well. The results from this interferometric investigation can be used to help mitigate the environmental impacts and potential consequences of land subsidence in the region.