# Improved Simplified Engineering Fault Displacement Hazard Evaluation Method for On-Fault Sites
## 1 Introduction
The papers [20; 21; 22] are examples of numerical rupture simulation, fragility evaluation and probabilistic safety analysis for fault displacement hazards. The fault displacement hazard issue for the nuclear site and the related international and national requirements and guidelines for the hazard evaluation and safety assessment are reviewed by the experts of the International Atomic Energy Agency (IAEA) [23]. Recognising the lack of documented case histories on PFDHA in the scientific and engineering literature, the IAEA in TECDOC-1987 [24] provides specific guidelines for PFDHA applications based on the three case studies above (Yucca Mountain, Diablo Canyon and Krsko site). Reference [23] documents a PFDHA benchmark analysis that consists of example applications made for a fictive site close to the Futagawa Fault System (i.e., the case for distributed fault displacement hazard) to identify the most critical aspects in the PFDHA models and demonstrate the analyses for understanding model differences. Based on the brief presentation of the state of the art and industrial practices, there is a strong tendency to use the PFDHA methods developed in [25; 26]. These methods require highly qualified experts and sufficient empirical data [27]. All existing applications of PFDHA methods are unique in that they are strongly influenced by the site's seismotectonic features, data availability and time. Although advanced fault displacement hazard analysis methods exist, simplified, conservative engineering hazard evaluation methods are often needed if an urgent decision should be made on the continuation of operation or implementation of protective measures, which are urgently needed. This is particularly true when the fault's activity is revealed during the operation, and the fault to be analysed is just below the site or crosses the critical infrastructure [1; 2; 3; 6]. The development and application of simple conservative hazard evaluation methods could also be motivated by insufficient data for sophisticated analysis. That is exactly the situation in the case of the Nuclear Power Plant Paks, Hungary site. The description of the neotectonics of the Pannonian Basin and the site vicinity area is given in [28; 29]. The paleoseismic investigations are documented in [30]. Briefly, the N-W end of an accurately mapped 27.9 km fault crosses the site, revealing a late-Pleistocene activity. In the trench, 20 ka old liquefaction-induced ground failure could be identified, indicating several earthquakes with magnitude \(M_{w}\gtrsim 4.5\) and a recurrence time of 1 ka. There are no historical or instrumental records of earthquakes in the site's vicinity area; neither the micro-seismic monitoring indicates activity nor the GPS monitoring shows a deformation tendency. According to the international and national nuclear safety regulations, if the Quaternary activity of the faults at the site's vicinity is suspected, the fault displacement hazard should be investigated and evaluated. The empirical evidence of the fault activity has been sufficient for the susception of hazard, but more is needed to perform a state-of-the-art probabilistic hazard evaluation. It is believed that the judgement of even the best experts and the use of sophisticated methods will not compensate for the lack of data. Since the site was the object of nearly continuous investigations during the last 30 years, a radical increase in evidence could not be expected from more site investigations. These circumstances motivated the research aiming to develop simple and conservative engineering hazard evaluation methods. The first attempt [4] has been made based on the Probabilistic Seismic Hazard Analysis for the site, which has been updated and reviewed by independent experts several times during the last 30 years. The seismic hazard disaggregation has been considered to define earthquakes' contribution to the hazard at fixed annual probability levels and their distribution in distance bins.