The shakemap procedure has been developed by the US Geological Survey (Wald et al., 1999b) and full information on the methodology and the latest version of the software are described in Worden et al. (2020) . The shakemaps shown in this site web portal have been generated using the new configuration of the ShakeMap procedure for Italy and fully described by Michelini et al. (2020).
More info about maps, can be found in the INGVterremoti post here (in Italian).
The Vs30 grid is available for download as a zip file here.