An investigation of Earth surface deformation by SBAS-InSAR analysis

Land subsidence, whether in its gradual down-settling form, creeping ground fracturing, or sudden sinkholes, is considered one of Iran's most catastrophic environmental challenges. The present study employed interferometric synthetic-aperture radar (InSAR) to detect land displacement in Garmsar City. The output maps reveal significant subsidence at 30 cm year-1 rates. According to the correlated subsidence map and piezometer data, groundwater harvesting for urban, industrial, and agricultural uses is primarily responsible for subsidence. High dependence on underground water resources and the absence of surface water resources in Iran's central regions have led to a radical decline in groundwater heads. For this target, 17 frames of images during 2015-2019 with a small temporal-perpendicular baseline were allocated and analyzed using the small baseline subset (SBAS). After removing unnecessary phases and noise, phase shift due to land deformation was extracted and converted to surface displacement. The InSAR analysis revealed a maximum of 37 cm and at least 33 cm subsidence for the Garmsar plain, and the average annual subsidence is estimated to be 36 cm, which is very close to the subsidence rate of the Tehran and Varamin plains. High-subsidence areas were generally located in the northern part of the Garmsar Plain, and subsidence rates decreased in the Southeast. The temporal and regional relationships between groundwater data and subsidence suggest that the general pattern of subsidence in the Garmsar Plain is caused by groundwater overexploitation, leading to widespread surface deformation. Since Garmsar is close to the capital, water resources are under pressure. By managing water resources in this area, this phenomenon will be reduced.