The role of uncertainty of model parameters in PSHA

Current approaches for the seismic hazard assessment, are mainly based on the classical formulation of the probabilistic seismic hazard analysis, widely known with the acronym PSHA. This procedure is able to compute the annual rate of exceedance of a set of ground motion intensity measures at a site of interest. During years, several efforts were performed for understanding and including the influence of uncertainties underlying the PSHA calculation. PSHA integral is a correct application of the total probability theorem, but it does not account for the uncertainties in model parameters which can be significant, since most of times they are derived from historical data and/or statistical catalogues. For this reason, this work aims to develop a robust semi-analytical formulation, able to assess how uncertainties in model parameters influence the seismic hazard curve’s reliability. The proposed mathematical procedure uses the reliability index and its standard deviation for computing a design hazard curve, whose points are characterized by a fixed accepted level of risk. Results show how uncertainties in model parameters affect the hazard curve’s dispersion, and how a better parameters’ knowledge allows defining lower design values, with the same assumed risk.