## 2 Study Area  
The study area is located in the Simav Basin in the northern Menderes Massif of western Anatolia, Turkiye (Figure 1). This region forms part of the Alpine-Himalayan orogenic belt and has undergone significant extensional tectonics from the late Neogene to the present. This setting provides a geodynamically active environment shaped by complex structural deformation and magmatic activity. Within this tectonic framework, the Demirci, Simav, and Dursunbey basins in the northeastern Menderes Massif have been the focus of extensive multidisciplinary research due to their pull-apart basin structures, magmatic-metamorphic evolution [23; 24; 25; 26; 27; 28], and rich geothermal resources. The Simav region and its surroundings have emerged as one of Turkiye's prominent geothermal energy zones. Numerous studies, including those by [29; 30], have evaluated the hydrogeochemical properties and reservoir potential of the area's thermal fluids. Geothermal resources in Simav are actively used for residential and greenhouse heating, as well as electricity generation. The heat potential of the Simav geothermal field is 1.3 \(\times\) 1014 kJ, and the electricity generation potential is 26 MW, with an average probability of 50%, while the most plausible value has been calculated as 19 MW [30]. The geological map and column section of the study area are presented in Figure 1 and Figure 2, respectively. The geothermal energy resources in the Simav Graben, where  
Figure 1: (**a**) The location of the study area on a regional map, modified from [31; 32]. (**b**) A 1:100,000-scale geological map of the Kütahya J21 and J22 quadrangles, modified from [33; 34]. The base elevation data are derived from the Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model (GDEM), Version 3, covering the N39E028 and N39E029 grids, with a spatial resolution of approximately 30 m. (**c**) Study area in the Simav Basin. the study area is located, are associated with lithologies that possess potential for heat generation, in addition to featuring permeable reservoir rocks and impermeable cap rocks essential for geothermal system development [35]. This study focuses on the migmatitic enginess of the Kalkan Formation, which constitute the basement rocks of the Menderes Massif and exhibit significant potential for RHP. The formation displays depth-dependent brittle and ductile deformation features [36; 37], indicating complex tectonometamorphic processes. Normal faults within the basin, along with intersecting transfer faults, are believed to facilitate the upward migration of geothermal fluids. The most lithologically suitable reservoir rocks for hosting geothermal fluids within the basin include the limestones of the Budagan Formation, marbles of the Balkbasi Formation, and quartzite layers within the Simav Metamorphites (Figure 2). The Budagan Limestone Formation contains interbedded banded schist layers, reflecting a complex depositional and metamorphic history [35; 39; 40]. The Balkbasi Formation is notable for its extensive fracturing and the development of micro- to macro-scale dissolution features, including karstic voids, which significantly enhance its capacity as a geothermal reservoir [34]. Additionally, the quartzite layers within the Simav Metamorphites demonstrate favorable reservoir characteristics due to their structural integrity and permeability [34; 35]. The Simav Graben, which cuts across the northern Menderes basins, trends predominantly in a north-south direction and is structurally defined by high-angle normal faults [41]. In the context of geothermal fluid transport within the graben, zones where transfer faults intersect with these high-angle normal faults are of particular significance, as they frequently serve as key conduits for fluid migration. Fault focal mechanism analyses of ongoing seismicity north of Simav further underscore the importance of regions where strike-slip and normal faults converge.