Challenges of building logic trees for probabilistic seismic hazard analysis

In the current practice of probabilistic seismic hazard analysis (PSHA), logic trees are widely used to represent and capture epistemic uncertainty in each element of the models for seismic sources and ground-motion prediction. Construction of a logic tree involves populating the branches with alternative models or parameter values, and then assigning weights, which together must represent the underlying continuous distribution. The logic tree must capture both the best estimates of what is known and the potential range of alternatives in light of what is currently not known. There are several scientific challenges involved in both populating the logic tree branches (for which new models often need to be developed) and in assigning weights to these branches. The most serious challenge facing this field now, however, may be a shortage of suitably qualified and experienced experts.