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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Low-seismicity regions such as the United Kingdom (UK) pose a chal-lenge for seismic hazard analysis in view of the limited amount of locally recorded data available. In particular, ground-motion prediction is faced with the problem that most of the instrumental observations available have been recorded at large distances from small earthquakes. Direct extrapolation of the results of regression on these data to the range of magnitudes and distances relevant for the seismic hazard analysis of engineered structures generally leads to unsatisfactory predictions. The present study presents a new ground-motion prediction equation (GMPE) for the UK in terms of peak ground acceleration (PGA), peak ground velocity (PGV), and 5% damped pseudospectral acceleration (PSA), based on the results of numeri-cal simulations using a stochastic point-source model calibrated with parameters derived from local weak-motion data. The predictions from this model are compared with those of previous GMPEs based on UK data, other GMPEs derived for stable continental regions (SCRs), as well as recent GMPEs developed for the wider European area. [ABSTRACT FROM AUTHOR]

Subduction earthquakes along the Pacific Coast of Central America generate considerable seismic risk in the region. The quantification of the hazard due to these events requires the development of appropriate ground-motion prediction equations, for which purpose a database of recordings from subduction events in the region is indispensable. This paper describes the compilation of a comprehensive database of strong ground-motion recordings obtained during subduction-zone events in Central America, focusing on the region from 8 to 14° N and 83 to 92° W, including Guatemala, El Salvador, Nicaragua and Costa Rica. More than 400 accelerograms recorded by the networks operating across Central America during the last decades have been added to data collected by NORSAR in two regional projects for the reduction of natural disasters. The final database consists of 554 triaxial ground-motion recordings from events of moment magnitudes between 5.0 and 7.7, including 22 interface and 58 intraslab-type events for the time period 1976-2006. Although the database presented in this study is not sufficiently complete in terms of magnitude-distance distribution to serve as a basis for the derivation of predictive equations for interface and intraslab events in Central America, it considerably expands the Central American subduction data compiled in previous studies and used in early ground-motion modelling studies for subduction events in this region. Additionally, the compiled database will allow the assessment of the existing predictive models for subduction-type events in terms of their applicability for the Central American region, which is essential for an adequate estimation of the hazard due to subduction earthquakes in this region. [ABSTRACT FROM AUTHOR]

The article counters the comments of Heriberta Castaños and Cinna Lomnitz on the authors' review of the subject about ground motions. It is believed that Castaños and Lomnitz are focused on criticizing standard probabilistic seismic hazard analysis (PSHA) in general. Analyzed is the comparison of motions recorded at one accelograph station and flipping a coin. Meanwhile, Castaños and Lomnitz are deemed correct that the maximum attainable levels of motion is being limited by finite strength of near-surface materials.