# Improved Simplified Engineering Fault Displacement Hazard Evaluation Method for On-Fault Sites
## 1 Introduction
The displacements were calculated by magnitude\(-\)displacement scaling correlations. It should be noted that the middle part of the Pannonian Basin is characterised as an area of diffuse seismicity. Since distance bins do not comply with the fault geometry, two options have been considered: (1) accounting for the distance bin that coincides with the site; and (2) considering all distance bins having essential contributions to the site's seismic hazard. The next effort was developing a method that followed the logic of PFDHA; however, the parameters of the fault activity were defined by the weighting of parameters of area sources of the PSHA (maximum magnitude, the rate of the minimum magnitude and the slope of the Gutenberg-Richter distribution) [5]. Since the considered fault is just below the plant, the principal displacement was calculated using the procedure in [26]. Since the site is located above the mapped fault line, the length of ruptures and their distances to the site should be accounted for in calculating the probability of rupture-site intersection. Several publications have addressed engineering methods for hazard analysis when the fault crosses the pipeline [31; 32], but no one is used for nuclear sites. The hazard evaluation studies for pipelines crossing a fault consider mainly uniform rupture distribution on the fault plane with size depending on the magnitude and create a probability geometrical distribution function. This concept was followed in [5], resulting in a more conservative hazard curve than in [4], despite expectations. These disadvantages of the simplified hazard evaluation methods in [4; 5] motivated the improvements presented in this paper. The paper presents first the sources of unnecessary conservatism in the methods for evaluating the fault displacement hazard of on-fault sites. It recognises that the displacement at the site depends in a complex manner on the geometrical relations between the site location on the fault line and the length and initial point of the rupture relative to the site. The length and initial point of the rupture can be considered independent random variables. In the paper, this interrelationship was investigated. Based on these considerations, a screening procedure was developed to identify ruptures crossing the site. This procedure is based on accurate geometrical limitations accounting for the mapped fault length, the relative position of the rupture ends relative to the fault end, the rupture length and the site location. The rupture length and the coordinate of rupture initiation are considered random variables. This results in a realistic estimation of the site intersection. Finally, the site displacement has been calculated accounting for the position of the rupture relative to the site. Several models exist for the displacement distributions of strike-slip faults, e.g., [26] and most recently [33]. The elliptical on-fault displacement distribution relationships in [26] have been considered in selecting the adequate displacement description that accounts for all geometrical circumstances (coordinate of the site and position of the rupture to the site). To demonstrate the effectiveness of the introduced improvements in the simplified hazard evaluation, site location-dependent hazard curves have been developed using the study data performed for Hungary's Nuclear Power Plant Paks site. The Paks site-specific data necessary for calculations are cited in the text. The hazard curves obtained by the improved evaluation procedure compared to those calculated by the conservative method in [5] justify the effectiveness of improvements and the avoidance of over-conservatism. The proposed improved engineering fault displacement hazard evaluation method in the paper represents the actual state of the research initiated by the Paks Nuclear Power Plant case and allows the resolution of the related safety issue of the Paks Nuclear Power Plant.