Determination of the block movements in the eastern section of the Gediz Graben (Turkey) from GNSS measurements

Abstract

The source parameters of an earthquake should be determined in detail to calculate deformations caused by that earthquake and to identify faults that are likely to break. Today, the GNSS method is frequently used to determine these source parameters. However, to date, no detailed study has been conducted for this purpose in the eastern section of the Gediz Graben. Therefore, in this study, the GNSS technique was used to determine the tectonic movements in the area between Alaşehir and Sarıgöl in the Gediz Graben. For the implementation of the GNSS technique, 11 benchmark sites, which had been previously established for different purposes in the area, were used, and the measurements were performed in 2013, 2014, and 2015. The GNSS measurements obtained at these sites were evaluated by GAMIT/GLOBK software, and the annual velocity values of the sites were obtained (with respect to the Eurasian plate). The resulting annual horizontal velocity values obtained at the GNSS sites ranged from 12 mm/yr to 27 mm/yr. It was observed that the sites with the highest vertical movements were within the graben. The annual vertical velocity value at the TRAZ site located in the east of the graben was obtained to be approximately −90 mm/yr. This site was followed by BGCL (-33 mm/yr) and AKCL (−13 mm/yr) toward the west of the graben. Furthermore, significant strain accumulations were derived in the study area, and their compliance with the tectonic structure of the region was revealed. The maximum and minimum principal strain parameters and the direction of maximum principal strain that provided the average drift and compression directions for the region were obtained to be 0.604 μs/yr, -0.375 μs/yr, and 11.27 °, respectively. Block modeling in the study area revealed that the annual strike slip ranged from 4 ± 1.2 mm/yr to 19.3 ± 0.6 mm/yr, and the dip slip varied between -23.3 ± 0.5 mm/yr and -16.0 ± 0.5 mm/yr.