Role of Seismic Zonation of the Northern Apennines, GMPEs and hazard software for PSHA evaluation in Emilia-Romagna, Italy

The results of various sensitivity analysis in probabilistic seismic hazard assessment indicate that the greatest impacting parameter in the computation are the choic of the seismic zonations and the ground motion prediction relations used; how many zonations and which attenuation relations are used and how they are combined in the branches of a logic tree can strongly affect the hazard results. Recent events in Italy highlighted unexpected large ground motions compared to the estimates obtained by probabilistic seismic hazard an alysesre presented by the national seismic hazard maps MPS04 (Meletti et al., 2008). For this reason, a preliminary version of a regional seismogenic zonation has been proposed (Martelli et al., 2014) for the Emilia-Romagna area based on some new regional seismotectonic studies. The new zonation is intentionally more detailed if compared to the national one that has been conceived to cover the entire Italian territory. The introduction of two transfer zones cutting the trend of the Apenninic zones of the national zonation represents the major novelty for the Emilia Romagna region. In both the zonations the boxes are characterized by homogeneous deformation informations inside (in terms of rupture mechanisms and geometry of faults: depth range, strike and dip). A 3D geometry has been defined for the new zones by introducing some seismogenic planes, i.e., 3D surfaces geometrically in agreement with the tectonic style dominating in the zone. A probabilistic seismic hazard analysis (PSHA) has been conducted aiming to compare the seismic hazard estimates, according to Cornell (1968) and using the software Crisis 2012 (Ordaz et al., 2012), obtained with the new zonation and the national ones. The new hazard estimates, although very preliminary, show interesting differenceswith respect to the national ones and point out the influence of a 3D geometry joint with a proper attenuation model in the expected ground motions on the surface.