## 1 Introduction
In the early nineties, a probabilistic seismic hazard assessment was made based on the full-scope geological, geophysical, seismological, and geotechnical investigations of the site. Since 1995, the site seismic hazard has been reviewed and updated every ten years in the frame of periodic safety reviews and the stress-test in 2011. Although the site is a licensed nuclear site, for the new Paks 2 plant to be constructed at the site, a full-scope site investigation and hazard evaluation have been implemented recently applying state-of-the-art techniques and methodologies. Presentation of the results of this extensive and complex investigations would exceed the frame of this paper. A brief summary is given below highlighting the scientific and practical motivation of the research. The Paks site is in the mid-part of Pannonian basin that is a region with typical diffuse seismicity (see, e.g., in [12]). As a result of the investigations for Paks nuclear site, it was known that the Kapos fault zone in central Hungary crosses the site vicinity area. Therefore, the fundamental question of former and recent site seismotectonic investigations was, whether some segments of the known fault zone at the site vicinity have been re-activated during Quaternary period. Recent paleoseismic investigations revealed that the eastern segment of the Kapos zone, the so called Dunaszentgyorgy-Harta fault zone shows neotectonic activity ([PERSON] et al. [11]). This is a broad, sinistral strike-slip shear zone consisting of predominantly NE-SW and ENE-WSW striking individual faults. The strike-slip kinematics of this shear zone is clearly indicated by the observed internal \"flower structure\" of the individual fault zones, as well as by the associated secondary fault pattern (Riedel faults). For the illustration of the geology and tectonic features of the near regional area (\(\sim\)25 km in radius [2] of the site), the schematic tectonost stratigraphic profile of the area and the definition of geological horizons (1-6) mapped in the 3D geological model Figure 1.  
The young geological deformations (after [PERSON] et al., [13]) and recent earthquakes (1995-2020) in the area 100 km in radius around the Paks NPP site are shown in Figure 2. On the other hand, there are no historical and instrumental earthquake records of any magnitude in the site vicinity, which is defined in line with [2] as a 5 km in radius scale. No event recorded within 10 km; 13 earthquakes within 25 km; 87 earthquakes within 50 km and 2484 known earthquakes within 100 km. Based on the 3D geological-structural model high-resolution 2D and pseudo-3D shallow high-resolution geophysical surveys were performed to locate the possible indications of Quaternary re-activation and near surface movement. The subsequent trenching proved a near surface movement with \(\sim\)10 mm vertical and \(\leq\)25 mm horizontal displacement with age about twenty thousand years. There are no historical or instrumental records of earthquakes in the site vicinity area. Moreover, the microseismic monitoring does not indicate activity during already three decades of monitoring and the GPS geodesy does not show significant tectonic movement (\(\leq\)0.1 mm/year) [2]). Considering the complex set of information that includes geological, geophysical, seismological, and paleo-seismological aspects and the mapped tectonic movement, a qualitative conclusion was made by [PERSON] et al. in [11] and in the site safety study [14] that the fault could not cause significant for nuclear safety surface movement. Here, the significance should be understood in sense of nuclear safety (see the safety guide SSG-9 [2]). Figure 1: Schematic tectonost stratigraphic profile of the area and the definition of geological horizons (1–6) mapped in the 3D geological model. The horizons surveyed are the following boundary surfaces and uncomformities: (1) top of basement, (2) M1 clastic Miocene top, (3) M2 marine Miocene top, (4) Endrôd top, (5) Algyô top, (6) Quaternary base.