A new Vs30 map for Italy based on the seismic microzonation dataset

In this study, we derive a large-scale Vs30 map for Italy starting from the global terrain geomorphologicalclassification based on normalized slope, local convexity, and surface texture (after Iwahashi et al., 2018). Thenovelty of the present work is the integration of a large amount of data from the Italian seismic microzonationdataset, consisting in about 35,000 borehole logs and 11,300 Vs profiles. The results of our analysis suggest thatthe geomorphological classes are correlated to subsoil lithologies and Vs30 values more than surface lithologicaltypes (after Amanti et al., 2008). As already done in Japan (Matsuoka and Wakamatsu, 2006), Greece (Stewartet al., 2014), Central and Eastern North America (Parker et al., 2017), and Pacific Northwest Region of NorthAmerica (Ahdi et al., 2017), we found a proxy dependence of Vs30 from slope gradient and elevation through alognormal linear regression model for each geomorphological class. A stepwise method allowed us to givemeaning and statistical robustness to the regression model dependencies. The polygons inconsistent with theIwahashi et al. (2018) approach (e.g., Meso-Cenozoic carbonate units of Apulian block and Hyblean Plateaurelated to the foreland domain) were replaced with the polygons of the lithological map (Amanti et al., 2008)and the associated Vs30 lognormal average values. Therefore, a hybrid raster Vs30 map was created with a spatialresolution of 50×50 m. The comparison with other previous maps shows how the forecast improves in terms ofboth accuracy and precision. For these reasons, the new Vs30 proxy-based map for Italy based on the seismicmicrozonation dataset represents a useful tool for improving several applications: ShakeMaps, stochastic eventbased hazard map, total hazard map, assessment of coseismic instabilities, seismic risk assessment for spatiallydistributed emergency and resilience systems. Vs30 raster maps and supplementary material are available in theResearch Data (doi:10.17632/8458tgzc73.1).