## 1 Introduction  
The Pannonian basin and its peripheral basins are an integral part of the Alpine orogenic system and were formed during the Miocene. Convergence between the Eurasian and Nubian plates generated a back-arc extensional environment, where orogenic terranes were disintegrated [1, 2]. During the deformational processes, the formation of extensional half-grabens and pull-apart basins has been diachronously accelerated in the western and eastern parts [3, 4, 5]. The heat flow together with the asthenospheric dome was elevated as high as 50-60 km beneath the central part of the Pannonian basin [2, 6, 7, 8, 9]. The tectonic inversion changed the surface relief, and thus controlled the gravity-driven flow systems in the basin fill. The Pannonian basin's heat flow value ranges from 50 to 130 mW\(\cdot\)m\({}^{-2}\), and its mean value is about 100 mW\(\cdot\)m\({}^{-2}\)[10, 6]. The temperature gradient varies between 40 and 50 K/km in the upper 5 km [11]. Geothermal exploration requires several controlling parameters like flow rate, fluid temperature, and water flow system. The third parameter is related to gravity-driven flows in porous Neogene sediments with a thickness of about 2 km [6] and overpressure-driven flow in the pre-Cenozoic basement or Early/Middle Miocene sediments [12]. This basin is the most promising geothermal prospect in Central Europe. The basin's evolution is related to peripheral basins that have developed surrounding it. On the northern edge, at the contact of an accretionary zone between the Outer Western Carpathians and the Inner Western Carpathians, the Eastern Slovak Basin (ESB) was opened. The ESB is an asymmetric basin with a depth of 9 km in the southeast. During the Miocene, the basin covered a relatively small area, which was characterized by dynamic subsidence of the basin. The sedimentation was accompanied by intensive volcanic activity around the basin. The heat flow value ranges from 100 to 125 mW\(\cdot\)m\({}^{-2}\)[13; 14; 15; 16] and temperature gradient varies between 40 and 52 K/km in the upper 3 km [17] (Figure 1). The water flow system is different compared to the Pannonian basin. The porous Neogene sedimentary layers of the ESB are less dominant. There are two pre-Cenozoic basement units (the Inacovo-Kricevo unit and the Humenne unit) which are hydraulically different potential aquifers. Their spatial position was confirmed by hydrocarbon trap exploration. The Inacovo-Kricevo basement unit was not a part of this study. Only a localized section of the Humenne Mesozoic Unit, 9.5% of the unit, occurs on the surface at the horst of the Humenne Mountains. A large part (978 km\({}^{2}\)) is located below the surface. The Humenne Mesozoic Unit is formed by carbonates of the Middle Triassic to the Middle Cretaceous. It represents a Paleoalpine unit, that has gone through several deformation stages and its structure is significantly different within the Western Carpathians. The difference lies in that in this region, the unit dips in the opposite direction and has a different geological composition compared to other areas [19]. The geological survey of the Humenne Mesozoic unit is based on several drilling and geophysical works. When exploring the geothermal energy of Slovakia, the horst of the HumenneMountains was defined as a prospective hydro-geothermal structure. The first use of hot springs in this area was in Sobrance Spa, the first record of which is from 1336. The geothermal water springs in the area of the spa were discovered by shallow boreholes with a depth of 120-400 m and verified by one 823 m deep borehole. The water temperature from the wells  
Figure 1: The Pannonian back-arc basin and its peripheral areas. The Eastern Slovak basin covers a significant part of Central Europe. The high heat flow (values in mW\(\cdot\)m\({}^{-2}\)) distribution in the basin is not uniform. The same is true for the aquifers. The Humenné Unit (blue mark) is one of the aquifers for geothermal use (modified after [6; 18]).