InSAR maps and time series observations of surface displacements of rock salt extruded near Garmsar, northern Iran
A large allochthonous sheet of Eocene rock salt is forming the Eyvanekey plateau west of Garmsar along the northern periphery of the Great Kavir basin. This salt extruded over the central plains of Iran, where the southward advancing front of the Alborz Mountains is offset by the NE–SW-trending Zirab–Garmsar strike-slip fault. Based on nine descending Advanced Synthetic Aperture Radar images, produced by the European Space Agency's ENVISAT satellite from 2003 to 2006, we used interferograms to map the displacement over 22 increments ranging in time from 2 to 18 months. To study the surface deformation at high temporal and spatial resolution, a small subset of interferograms was used to map the mean velocity of surface deformation. The results suggest that the top of the salt is subsiding continuously at rates that depend on the season. The surface displacement rate throughout the region ranges from subsidence of −40 to −50 mm a−1 to uplift of 20 mm a−1. The agricultural lowlands, where groundwater extraction for irrigation exceeds recharge, are subsiding faster than the salt sheet. Correlation of surface displacements with active folds and seismic faults around the salt sheet also suggests that the study area is undergoing active deformation.