Investigation of the Söke sub-basin using the direct current resistivity method

The Büyük Menderes Basin consists of the Söke, Aydın, Didim and Bafa sub-basins. The aim of this work is to determine the electrical and hydrogeological properties of the relatively shallow subsurface in the Söke sub-basin by a direct current resistivity survey carried out using the Vertical Electrical Sounding (VES) technique at 19 measurement points in the SW-NE direction. In this context, the apparent resistivity data collected in the study were evaluated using one-dimensional (1D) and two-dimensional (2D) inversion techniques. As a result of the 1D inversion, layer parameters such as resistivity and thickness were determined for each VES point and the vertical resistivity distribution of the subsurface was obtained. The 1D solution revealed that the thickness of the alluvium is greater in the south-western sections of the study area than in the north-eastern sections. In addition, a low resistivity zone characterized by high salinity and degradation was identified at a depth of approximately 30-50 m and extends approximately 30 km to the northeast. The 2D inversion model derived from the VES data agreed with the 1D results and showed a low resistivity structure and a degraded zone at relatively shallow depth. Besides, the 2D inversion also identified a lateral variation in resistivity, indicating undulations. Other important parameters for understanding the physical properties of the subsurface formations and modeling the subsurface structures were calculated. These parameters include equivalent resistivity and thickness, longitudinal and transverse resistivity, anisotropy coefficient, effective formation resistivity, reflection coefficient, resistivity contrast and protective capacity rating (PCR). The results show that the subsurface formations in the Söke sub-basin have heterogeneous and distinct electrical properties. In particular, significant deviations in parameters such as longitudinal conductivity and transverse resistivity indicate differences in the water content and permeability of the subsurface. High values for equivalent resistivity and low values for longitudinal conductivity correspond to dry and impermeable zones, while low values for equivalent resistivity and high values for longitudinal conductivity correspond to water-bearing and permeable zones. The PCR values, most of which were classified as "excellent"," indicate that the basin has a high water-bearing capacity and that suitable formations for water conservation are present. It is expected that the geophysical analysis results presented in this paper will provide a solid foundation for effective water resource management and hydrogeological modeling in the region, thus making an important contribution to future studies on water resource management.