Investigation of deformations with the GNSS and PSInSAR methods

The Aegean graben system (AGS) involves a series of parallel faults that extend perpendicularly to the Aegean Sea, forming plains and mountains. The plains in this system move downwards due to gravity acting on the active faults that delimit them. The major grabens in the Aegean region are, from north to south, the Edremit Gulf, Bakırçay, Simav, Gediz, Küçük Menderes, Büyük Menderes, and Gökova Gulf. The surface deformation and tectonic movements in the Büyük Menderes Graben were investigated in this study using both global navigation satellite system (GNSS) and Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) methods. The results were compared. Firstly, the measurements from eight GNSS stations that continuously make observations on the Büyük Menderes Graben were analyzed, with the aim of determining the tectonic movements in the graben and the velocity field of the region. Additionally, movements in the line-of-sight (LOS) direction of the region were determined by performing PSInSAR analyses covering the entire Büyük Menderes Graben region. From analysis of the GNSS measurements, Eurasian plate fixed/ITRF08 velocities of the stations were obtained. It was found that, horizontally, the study region is moving to the southwest at a rate of 25–28 mm/year. Vertically, velocity values in the ( +) direction were observed at stations BOZD, AYD1, and KUSD. The highest velocity was at BOZD, at 2.42 mm/year, while the lowest velocity was at AYD1, 0.71 mm/year. Velocity values in the ( −) direction were observed at stations DNZ1, PAMU, AYDN, DIDM, and DIDI. The highest velocity was observed at PAMU, at − 5.12 mm/year, while the lowest velocity was at AYDN, at − 0.06 mm/year. Thirty-four synthetic aperture radar images, detected between 13.01.2016 and 16.12.2018, were used in the PSInSAR analysis. Examination of the annual velocity values of the study region in the LOS direction revealed annual subsidence values of up to 23 mm and annual uplift values of up to 13 mm. Additionally, subsidence was detected at the center of the graben, while uplift was detected north and south of the graben. Comparison of the results from the two methods showed that they were in good agreement.