Converting PSH estimates in terms of ground motion intensity into macroseismic intensity estimates

Methodological aspects relative to the conversion of probabilistic hazard evaluations in terms of ground motion intensity into hazard in terms of macroseismic Intensity. As a first step, the probabilistic relationships between ground motion intensity and macroseismic intensity are critically re-examined to account for the different formal properties of these two dimensions of the earthquake intensity. Then these relationships are coherently considered in the conversion of hazard curves by accounting for the inherent binning of macroseismic intensity values and of their inherent probabilistic nature. It is shown that approximate procedures currently used to provide this conversion may provide biased outcomes when the dispersion of values relative to ground motion intensity corresponding to macroseismic Intensity is dismissed or not properly accounted for. The impact of this possible bias is evaluated by considering the seismic hazard at reference site condition at the city of L’Aquila in Central Italy.