Spatiotemporal relation of RADAR-derived land subsidence with groundwater and seismicity in Semnan—Iran

Abstract

Due to excessive harvesting of underground water resources in many important aquifers inside Iran, ground subsidence is occurring at different speeds. In present study, InSAR processing was applied to identify land displacement by using Sentinel-1A. For this target, 17 frames of images during 2015–2019 with small temporal-perpendicular baseline were allocated and using SBAS approach were analyzed. After removing unnecessary noise and phases, phase shift due to land deformation is extracted and then converted to subsidence. Besides SAR images, fluctuations of groundwater were analyzed using piezometric data for last 10 years. Then the spatial pattern relationship between subsided regions and underground water resources as well as urbanization was investigated. Throughout this period, all datasets reveal 125 km2 bowl subsidence in a maximum rate of 10 cm/year. Generally, areas with high rates of subsidence are located between the industrial town and city of Semnan over clay foundation with high rates of groundwater head decline. Moreover, surveying the piezometers and landuse change map obtained from Landsat indicates that due to the intense groundwater withdrawal as a result of industrialization and urbanization, the maximum annual decline of groundwater head at 123 cm/year is detected. Our preliminary investigation shows some spatiotemporal positive correlation between the subsidence and seismicity of the area. Considering the fragility of arid ecosystems and increasing the population of Semnan, it is recommended that the development of industries with high water consumption is prevented and the groundwater resources policies should seek to strictly reduce overusing of groundwater in agricultural lands and urban areas.