Seismic microzoning map. Approaches, results and applications after the 2016–2017 Central Italy seismic sequence

The Seismic Microzonation of level 3 (SM3) is nowadays a world-wide accepted tool for the mitigation of seismic risk. The SM3 is a complex process involving different disciplines ranging from Geology and Applied Seismology to Structural and Geotechnical Engineering. The outcome of a SM3 is presented on a zoning map in terms of a selected ground shaking intensity parameter and susceptibility to main ground instability (soil liquefaction, settlements, landslides, fault ruptures). In an advanced SM3 study for a given area, four main interdisciplinary steps can be recognized: (1) definition of the reference input motions, (2) construction of the subsoil model, (3) performing of numerical analyses and computing of amplification factors, (4) identification of zones with different geotechnical hazard potential and drawing up of the SM3 map. After the 2016–2017 Central Italy seismic sequence, intensive studies have been performed to obtain SM3 maps in 137 municipalities most damaged by the earthquakes. The aim of these studies has been to obtain a clear background on site effects to perform a correct reconstruction of the municipalities. In the paper, main results and critical issues of the above-mentioned steps of SM3 procedure are discussed together with some remarks on the use of SM3 output in supporting seismic design for reconstruction.