The sustainable utilization of geothermal energy mostly depends on the characteristics of the geothermal resource from which it is extracted. Among others, detailed geological modeling is a key factor for estimating the potential of a geothermal resource. This research focuses on the modeling and reconstruction of the geological setting of the Daruvar thermal spring area using geophysical techniques. An integrated geophysical approach based on electrical resistivity tomography (ERT) and both active and passive seismic (MASW and HVSR) methods was used. Based on ERT results and the stratigraphic logs of the wells in Daruvar, three resistivity layers/geological units were identified. The deepest layer with resistivity < 150 Ωm is the Triassic carbonate that constitutes the thermal aquifer. Sharp lateral variations in the resistivity distributions within the bedrock were interpreted as fault damage zones saturated with thermal waters. Integrating the results of the seismic methods, the thickness of the first seismic layer that corresponds to the Quaternary cover was estimated from 5 to 20 m. Here, results of the geophysical investigations were combined into a 3D geological model highlighting the occurrence of subvertical N-S and E-W trending faults in the Daruvar spring area. The N-S-trending fault was interpreted as a fault plane parallel to the regionally mapped Daruvar fault. This fault juxtaposes the Triassic carbonate complex of the thermal aquifer with a Neogene sedimentary sequence of significantly lower permeability. Neogene–Quaternary tectonic activity further increased the fracturing and the permeability field in the Daruvar spring area, as proven by the smaller scale E-W faults and the well logs. This fracture network permits a quick upwelling of thermal fluids resulting in thermal springs with temperatures up to 50 °C. This work proves that the construction of a detailed geological model is crucial for assessing the reservoir and fault geometries in thermal systems hosted in fractured carbonate rocks.

Landfills situated in karst terrains pose unique sustainability challenges due to the complex geological characteristics of these environments. This is mainly due to the well-developed underground drainage systems, including discontinuities and caves that can quickly transport contaminants over long distances, reaching the water sources and ecosystems. The focus of this study is on multi-geophysical assessment incorporating electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) to evaluate the volume of the waste and to delineate the contact between the waste material and the karst, offering a more comprehensive view of subsurface conditions. The presented examples include geophysical mapping of the landfills Sodol and Sorinj, situated in the immediate vicinity of sensitive water bodies, increasing the potential risk of environmental contamination. At both sites, the boundary between waste material and bedrock was clearly delineated. Bedrock was identified with P-wave velocities of approximately 3000 m/s at Sodol Landfill and 2000 m/s at Sorinj Landfill. Waste material, observed at both sites, exhibited electrical resistivity values up to 120 Ω·m. The combined use of ERT and SRT provides extensive coverage of the landfill area, surpassing what can typically be achieved through traditional methods such as boreholes or excavations. Overall, the obtained results show promising potential for using integrated geophysical methods to accurately characterize landfill sites in karst terrains, thereby improving environmental protection strategies in karst regions and contributing to sustainable waste management.