A proposal for a new parametrization of historical intensity data providing a better handling of uncertainties

In recent times a great deal of research was aimed to the reduction of uncertainties on Probabilistic Seismic Hazard Analysis (PSHA). Most attention was paid to the role of Ground Motion Prediction Equations (GMPEs), while no studies were devoted to a possible larger source of uncertainties: the historical catalogues of earthquakes. In areas where historical catalogues provide a many centuries long record and surface geology does not permit at the moment to have complete catalogues of seismogenic faults, their use is unavoidable for estimating seismicity rates required for PSHA. Their use is also gaining popularity as an independent tool for the estimation of PSHA (D'Amico and Albarello, 2008) or for their use for validation purposes (Stirling and Petersen, 2006; Mucciarelli et al., 2008). This paper proposes an alternative way for the parametrization of historical macroseismic intensity and then discusses which is the real impact of starting uncertainties in intensities on the final uncertainties on PSHA.