Risk CDT – Understanding epistemic uncertainty captured in seismic hazard assessments for critical infrastructure

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This is a project within the multi-disciplinary EPSRC and ESRC Centre for Doctoral Training (CDT) on Quantification and Management of Risk & Uncertainty in Complex Systems & Environments, within the Institute for Risk and Uncertainty. The studentship is granted for 4 years and includes, in the first year, a Master in Decision Making under Risk & Uncertainty. The project includes extensive collaboration with prime industry to build an optimal basis for employability.

Safety critical infrastructure, such as nuclear power plants and waste repositories, and large-scale hydroelectric schemes, require seismic hazard assessments to be conducted as part of the regulatory process, even in low-seismicity areas such as the UK. The purpose of these assessments is to estimate the probabilities that various levels of earthquake ground shaking will be surpassed during a given period. For regulatory acceptance of the project it is necessary to demonstrate that these hazard levels are clearly below the seismic loading that was considered in the design or, in more recent studies, to show that the risk of a critical damage state (e.g. damage to the reactor core) is lower than a certain threshold.
Because of the rarity of earthquake ground motions of engineering significance near to specific locations (even those in the most seismically-active regions, e.g. Japan) seismic hazard assessments are associated with considerable uncertainty. Consequently, it is difficult to show that the hazard or risk levels clearly respect the imposed regulations. Coupled with this is the fact that many of the inputs to the hazard assessments rely on subjective judgments of expert groups, whose opinions are commonly captured through weighting different hypotheses in the framework of a probabilistic logic tree.

The aim of this project is to better understand the sources of uncertainty within seismic hazard assessments, in particular those related to the estimation of strong ground motions at a given site from a particular earthquake. This aspect is often shown to be one of the key drivers of uncertainty. The project will investigate how this uncertainty can be measured, captured and checked to see that it is appropriate given the level of knowledge for a particular region. The overall aim of the project is to develop a method that moves away from principally subjective assignments towards a more objective, repeatable and defendable assessment of logic-tree weights for a given site.

The project will consist of analyses of large databases of earthquake data, principally strong-motion records and their associated parameters, as well as statistical investigations of previously published seismic hazard assessments and their components (e.g. ground-motion models). A key initial step of the project will be to compare and judge the various techniques that have recently been proposed to capture the ‘appropriate’ level of epistemic uncertainty within ground-motion models, which include both approaches based on improving expert elicitation and also statistical techniques. Based on this analysis an improved framework for the construction of a composite ground-motion model will be proposed that is applicable to site-specific studies, such as those for nuclear power projects, as well as regional hazard assessments for use in seismic design codes for normal structures, e.g. residential buildings.
Through the planned interaction with industrial partners (e.g. via secondments and participation in project meetings) the student will gain experience of practical application of their research and networking opportunities. Engineering seismology and earthquake engineering are international disciplines with much cross-border collaboration and hence there will be opportunity for the student to attend and present their research in overseas conferences and workshops and to interact with a wide variety of people. The outcomes of this project have the scope to change significantly seismic hazard assessments for critical infrastructure.