GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 Seismic hazard assessment at the regional scale: the example of Emilia-Romagna G. Carloni 1 , L. Martelli 2 , G. Vignaroli 1 , G. Viola 1 1 Università di Bologna – Dipartimento di Scienze Biologiche, Geologiche e Ambientali 2 Regione Emilia-Romagna – Area geologia, suoli e sismica Introduction The propagation velocity of shear waves in the ground (VS) is a fundamental parameter to improve the knowledge of seismic risk and mitigation thereof. Knowing how VS changes with depth, for example by defining a mean VS equivalent value VSeq for the subsoil directly overlying the seismic bedrock 1 , is necessary to constrain the seismic acceleration and velocity at the surface, which is required for Seismic Microzonation (MS) procedures (MS Working Group, 2008). By acquiring and storing in well-structured databases VS data from much of its territory, the Regione Emilia-Romagna has systematically mapped the VSeq values. At the same time, it also produced a map of subsoil classes (A to E, according to the NTC18) and of the maximum expected acceleration a max at each acquisition site. Here, we propose an estimation of the expected maximum acceleration at the surface for a return period of 475 years, by applying the level 2 MS criteria as per the regional guidelines (Tento et al., 2014; DGR 476/2021 and DGR 564/2021). V S calculation for the Emilia-Romagna territory The calculated V S values derive from the Emilia-Romagna regional geognostic database integrated with numerous MS studies at the local municipal scale and including surveys specifically carried out for the reconstruction work in the aftermath of the 2012 seismic sequence. V S values were stored as V Seq : = =1 ∑ ℎ where H is the depth of the seismic bedrock, n is the number of considered layers, h i is the thickness of the i-th layer and V Si is the shear wave velocity in the i-th layer. 1 Seismic bedrock can be defined as a lithological unit characterized by a rigid behaviour, i.e., by a V S significantly greater than that of the overlying succession or cover (e.g. V Sbs /V Seq >2÷3); technical standards (EN 1998-1, 2004; NTC, 2018) define the seismic bedrock as compact rock characterized by V S >800 m/s (subsoil category A).