Effects of Magnitude Uncertainties on Seismic Hazard Estimates

The standard probability tree methodology of probabilistic seismic hazard assessment (PSHA) allows for the explicit treatment of many kinds of uncertainty. These include both epistemic uncertainty (e.g., uncertainty in the parameters of the frequency-magnitude relation for a given source region, and in the form and parameters of relations for attenuation of strong shaking) and aleatory uncertainty (i.e., natural variability about the fitted relations). However, the analysis of uncertainty seldom extends to a formal treatment of uncertainties in the data on which the relations are based. Such uncertainties are not readily captured by the probability tree approach; rather they affect the quality of the fitted relations, and as shown below, may be a cause of bias or of spurious variability.