- © 2013 by the Seismological Society of America
The purpose of a site‐specific probabilistic seismic‐hazard analysis (PSHA) is to characterize the potential levels of ground shaking that could be experienced due to future earthquakes in the region. The output from such a PSHA, usually expressed in the form of acceleration response spectra at different annual frequencies of exceedance, may be used as the basis for earthquake‐resistant design, to check the seismic margins for an existing design, or as input to complete seismic probabilistic risk analysis. In a regulatory environment, such as for nuclear facilities, it is of particular importance to demonstrate confidence in the estimated levels of ground motions. This is achieved through three key features of the PSHA study: (1) the study is conducted by suitably qualified teams, using an appropriate methodology; (2) all sources of uncertainty are identified, quantified, and incorporated into the calculations; and (3) calculations that provide output that is used directly in the PSHA model, and the PSHA calculations themselves, are subject to Quality Assurance (QA). After the accident at the Fukushima Daiichi nuclear power plant following the Tohoku earthquake in March 2011, it can be expected that the imperative to provide such regulatory assurance with regards to earthquake hazard has been brought into even sharper focus.
This brief paper discusses how the three requirements for regulatory assurance listed above can be met in practice. The focus of the paper is the challenge of providing QA checks on the actual hazard calculations, not so much in terms of the core calculations performed within the PSHA software, but rather in checking the correct implementation of the logic trees representing the full range of uncertainty in the seismic source characterization (SSC) and ground‐motion characterization (GMC) models. A promising approach for addressing this requirement is illustrated with a practical example from a PSHA project for the Thyspunt nuclear site …