ShakeMaps for three relevant earthquakes in the Southeastern Alps: Comparison between instrumental and observed intensities

We test a recently developed ShakeMap model for the Friuli Venezia Giulia (NE Italy) region (Moratto et al., 2009) by comparing the macroseismic observations, related to three past earthquakes (Cansiglio 1936, Friuli 1976 and Bovec-Krn 1998) which occurred in this region, with the instrumental intensities obtained from the ShakeMaps, and based on synthetic seismograms computed from available source models of these events. Because a comparison requires that the simulation resembles as close as possible the real situation, ShakeMaps are computed from synthetics calculated at receivers placed at the sites where the recording instruments are already operative and at the sites where the instruments are going to be installed in the near future. Since the available instrumental recordings are very few, the resulting instrumental intensity maps are compared with the macroseismic observations wherever the latter are available. We make use of various relationships between the ground motion parameters and the macroseismic intensity during the comparison. The best results are obtained when the macroseismic intensities (I ≤ VII) are estimated using the relationship proposed by Faenza and Michelini (2010).