A probabilistic seismic hazard analysis (PSHA) has been conducted as part of the Safety Case justification for a new-build nuclear power plant in the UK. The study followed a cost-efficient methodology developed by CH2M and associates for safety-significant infrastructure where high-level regulatory assurance is required. Historical seismicity was re-evaluated from original sources. The seismicity model considered fourteen seismic sources which, when combined, formed six alternative seismic source models. Separate models for the median ground-motion and aleatory variability were considered. The median groundmotion model comprised a suite of ground-motion equations adjusted to the sitespecific conditions using V S-kappa factors. A partially non-ergodic sigma model was adopted with separate components for the inter-event variability, and singlestation intra-event variability, adjusted by a partially ergodic site-to-site variability term. Site response analysis was performed using equivalent-linear random vibration theory with explicit incorporation of the variability in the ground properties using Monte Carlo simulations. The final PSHA results were obtained by convolution of the hazard at the reference rock horizon with the site amplification factors. The overall epistemic uncertainty captured by the logic tree was assessed and compared against results from earlier PSHA studies for the same site.

The United Arab Emirates (UAE) is undergoing very rapid development with one of the highest construction rates in the world. A number of studies of the seismic hazard in the UAE have been published in recent years, presenting diverse interpretations of the earthquake threat in this country of relatively low local seismicity, creating confusion regarding appropriate seismic design levels. Although there is inevitably considerable uncertainty associated with the assessment of seismic hazard in such a region, those studies indicating rather high levels of ground motion associated with a 475-year return period are found to be the result of inappropriate seismic source zonations that spread seismicity from the Zagros region of Iran into the Arabian Peninsula. A new probabilistic seismic hazard analysis is performed within a logic-tree framework, and the results displayed as uniform hazard spectra for rock sites in the cities of Abu Dhabi, Dubai and Ra's Al Khaymah in the UAE. The results support the UBC 1997 classification of the two former cities in Zone 0 (no seismic design required) whereas in Ra's Al Khaymah Zone 1 would be appropriate.

This article presents a streamlined approach to seismic hazard assessment aimed at providing regulatory assurance, whilst acknowledging commercial and program constraints associated with the development of safety-critical facilities. The approach was developed based on international best practice and followed the spirit of the Senior Seismic Hazard Analysis Committee (SSHAC) Level 2 requirements, while incorporating the key features of the SSHAC Level 3 process aimed at achieving regulatory assurance, but with a more flexible implementation. It has also benefited from experience gained by others regarding the implementation of the SSHAC process in projects in the USA, Switzerland and South Africa. The approach has been successfully applied as part of the Safety Case for the new-build nuclear power plant at Hinkley Point, UK. The proposed approach can be considered as a cost-effective solution for the seismic hazard evaluation of safety-significant facilities where a high level of regulatory assurance is required.

A key task when developing a ground-motion model (GMM) is to demonstrate that it captures an appropriate level of epistemic uncertainty. This is true whether multiple ground motion prediction equations (GMPEs) are used or a backbone approach is followed. The GMM developed for a seismic hazard assessment for the site of a UK new-build nuclear power plant is used as an example to discuss complementary approaches to assess epistemic uncertainty. Firstly, trellis plots showing the various percentiles of the GMM are examined for relevant magnitudes, distances and structural periods to search for evidence of “pinching”, where the percentiles narrow excessively. Secondly, Sammon’s maps, including GMPEs that were excluded from the logic tree, are examined to check the spread of the GMPEs for relevant magnitudes and distances in a single plot. Thirdly, contour plots of the standard deviation of the logarithms of predicted ground motions from each branch of the logic tree (σµ) are compared with plots drawn for other relevant hazard studies. Fourthly, uncertainties implied by a backbone GMM derived using Campbell (2003)’s hybrid stochastic empirical method are compared to those of the proposed multi-GMPE GMM. Finally, the spread of the percentile of hazard curves resulting from implementing the GMM are examined for different return periods to check whether any bands of lower uncertainty in ground-motion space result in bands of lower uncertainty in hazard space. These five approaches enabled a systematic assessment of the level of uncertainty captured by the proposed GMM.

Figures 3, 4, 5 and 6 were incorrectly published with formatting errors and have been updated.Original article has been corrected.