Mashhad Subsidence Monitoring by Interferometric Synthetic Aperture Radar Technique

A number of regions around the world have suffered severe subsidence due to groundwater withdrawal. Mashhad as one of the largest municipalities in Iran has suffered subsidence due to deep groundwater overextraction. Land subsidence in this area can be destructive for urban infrastructures and can create serious environmental issues and structural damages. So, the aim of this research is to precisely determine the uninterrupted vertical subsidence in Mashhad by Permanent Scatterer InSAR technique and also to assess the previous reports on the study area. We complement previous works using more accurate data and procedure in an urban area. Furthermore, we considered geotechnical properties which was not focused in the previous studies. For this purpose, 69 descending and ascending C-band radar images, provided by relatively high-resolution Sentinel-1A satellite, were used to estimate the deformation-trend of the interest area. The method was applied to the images spanning October, 2014, and February, 2017 investigating land subsidence. The assessment procedure demonstrated a high-rate of subsidence in northwest of Mashhad with the significant deformation of 140 mm/year. The outputs were validated using in-situ measurements data and hydraulic head variations respecting piezometric data from groundwater wells. Subsequently, the geotechnical properties of the chosen area were considered to interpret the results. It was illustrated that the land subsidence in the case study is brutally continuous and there is no decrease on the deformation rate.