Revision of seismic hazard in emilia-romagna based on a new seismogenic zonation of the northern apennines

Recent events in the Emilia-Romagna region highlighted unexpected large ground motions and this aspect caused criticism to the estimates obtained by probabilistic seismic hazard analyses represented by the national seismic hazard maps MPS04 (Stucchi et al., 2011). For this reason, some regional seismotectonic studies are in progress for this area, and a preliminary version of a new regional seismogenic zonation (see Fig. 1a) has been proposed (Martelli et al., 2014). This new zonation is, in the studied area, intentionally more detailed if compared to the national one (Meletti et al., 2008) that has been conceived to cover the entire Italian territory. The introduction of two SW-NE transfer zones cutting the NW-SE trend of the Apennine zones of the national zonation represents the major novelty for the Emilia-Romagna region. The boxes of Fig. 1a represent the superficial projection of rock volumes characterized by homogeneous deformation inside (in terms of failure mechanisms and geometry of faults: depthrange, strike and dip). In the present work, a probabilistic seismic hazard analysis (PSHA) has been conducted aiming at comparing the seismic hazard estimates based on the new zonation[obtained according to Cornell (1968) in the software formulation of Crisis 2012 (Ordaz et al., 2012)] with the national ones. In agreement with the Italian zonation, also the new seismogenic zones (SZs) have been initially considered in 2D. Successively, a 3D geometry has been defined for the new zones by introducing some seismogenic planes, i.e., 3D surfaces with a geometry in agreement with the tectonic style dominating in the SZ. The new hazard estimates, although very preliminary, show interesting differences with respect to the national ones and point outthe influence of a 3D geometry joint with a proper attenuation model in the expected ground motions on the surface.