Surface deformation over the buried Nasr Abad salt diapir, Central Iran using interferometric synthetic aperture radar data

Abstract

ABSTRACTThis 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 diapirs in Iran and could be ideal site for oil/gas storage and industrial waste disposal. In this study, we use 40 advanced synthetic aperture radar (ASAR) images from Environmental Satellite (EnviSat) to analyse surface displacement rates of Nasr Abad diapir and its surrounding regions. A time series of line-of-sight (LOS) displacements on the residual cap above the buried diapir were obtained from both descending and ascending images between 2003 and 2010 by applying the Small-BAseline Subset (SBAS) technique. Tropospheric artefacts in the displacement interferograms were mitigated using the power-law correction method in Toolbox for Reducing Atmospheric InSAR Noise (TRAIN) software. Finally, the data for temperature, precipitation, and tidal forces were correlated with the time-series displacement results of four points that located on the residual cap. Our results indicate that surface above the diapir and an area of about 2 km2 subsided with maximum LOS velocity of about 7 mm year−1 for ascending images and 5 mm year−1 for descending images. The amount of vertical subsidence derived from LOS decomposition in reactive stage of Nasr Abad salt body is about 7 mm year−1. Comparing the temperature and precipitation data with the time series of displacement confirmed that the salt expands when temperatures increases and that salt flow accelerates when it is wet. The displacement pattern retrieved from InSAR analysis is in good agreement with intervals near maximum and minimum solid earth tides. Monitoring the activities of the Nasr Abad region over 7 years shows that the region of surface subsidence is confined to the area along the Khurabad and AbShirin-Shurab Fault zones in the southern Central Basin.