Abstract

This comment discusses some heuristic biases with respect to the correct treatment of uncertainty in probabilistic seismic-hazard analysis (PSHA) observed in the recent article titled “Why Do Modern Probabilistic Seismic-Hazard Analyses Often Lead to Increased Hazard Estimates” by Julian J. Bommer and Norman Abrahamson. I show that the distinction between aleatory variability and epistemic uncertainty in seismic-hazard analysis represents a think model rather than an objective property of earthquake occurrence. It is demonstrated that the separation between epistemic uncertainty and aleatory variability is model dependent. I show that a correct application of this think model does not lead to an increase of hazard estimates, because the total uncertainty to be incorporated into a PSHA model is bounded by the uncertainty observed in the real world. Ground-motion variability cannot be statistically treated as an inherent property of earthquake occurrence. Its statistical measures are model dependent. A refined definition of the terms epistemic uncertainty and aleatory variability is suggested. Furthermore, the paper addresses the observation that the methodology of traditional PSHA may lead to a violation of the energy conservation principle. Finally, a summary of some of the most problematic areas of current PSHA methodology is given.

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