Seven years of surface deformation above the buried Nasr-Abad salt diapir using InSAR time-series analysis, Central Iran

This study employs interferometric Synthetic Aperture Radar (InSAR) data sets to monitor the surface deformation of the Nasr-Abad buried salt diapir in the Central Basin of Iran. The Nasr-Abad salt diapir is one of the largest buried salt diapir in Iran and could be ideal site for oil/gas storage and industrial waste disposal. Forty ENVISAT Advanced Synthetic Aperture Radar (ASAR) images acquired during 2003-2010 were used to monitor surface activities of this diapir and its surrounding regions in that time window. One hundred and one interferograms were generated from both descending and ascending orbits by applying the Small-BAseline Subset (SBAS) method. Tropospheric artefacts in the displacement interferograms were mitigated using the power law correction method in TRAIN software. A time series of line-of-sight (LOS) displacements on the residual cap of Lower Red Formation above the buried diapir was also generated as well as the area. Finally, the data for temperature, precipitation, and tidal forces were correlated with the time-series displacement results of four points A, B, C, and D that located on the residual cap. Our analyses of our data indicate that surface above the diapir and an area of about 28 square kilometres subsided with maximum LOS velocity of about 7 mm/year for ascending images and 5 mm/year for descending images. Comparing the temperature and precipitation data with the time-series of displacement confirmed that they correlated with the same seasonal effects. Monitoring the activities of the Nasr-Abad region over 7 years shows that the region of surface subsidence is confined to the area that relates directly to the geological structures of the region.