GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 2.2 GNGTS 2024 available site parameters on the residual value were invesCgated. The distribuCons of the residuals (Fig. 1) show a posiCve mean term, which clearly indicates an underesCmaCon of empirical amplificaCon by the syntheCc approach. The mean underesCmaCon term increases with the considered period interval, while the associated uncertainty ( ! of such distribuCons) is almost constant with respect to the period. The distribuCons also show negaCve tails, which are related to those sites having experimental de-amplificaCon of ground moCon. Despite the lack of detailed geological informaCon for the studied sites, the uniform geo- l i thologi cal c lass ificaCon of the naConal map at 1:100.000 scale ( hbp: // www.pcn.minambiente.it/mabm) revealed that most of the sites (65%) for which the syntheCc approach underesCmates the observed amplificaCon are located on alluvial deposits and chaoCc sedimentary complexes, while the sites for which an overesCmaCon was calculated by FA_syn are located on bedrock formaCons and mostly correspond to sites with the FA_exp < 1. These preliminary results suggest that the amplificaCon maps produced prior to the SERENA project using the syntheCc approach may significantly underesCmate the experimental ground-moCon amplificaCons. Therefore, the approach should be improved so that the FA_syn values can cover a wider range (max FA_syn >> 2). Furthermore, the analysis of the residuals suggests that larger discrepancies between the experimental and syntheCc esCmates occur for long-period amplificaCons, which may be caused by: i) bedrock definiCon in 1D simulaCons for those sites located on large intermountain basins characterised by large bedrock depths (> 100 m) and ii) 2D/3D site effects. Fig. 1 - DistribuCon of residuals between median FA_exp and Fa_syn values (in natural logarithmic units) as a funcCon of period: short (FA1 blue), intermediate (red) and long periods (green). References Falcone G., Acunzo G., Mendicelli A., Mori F., Naso G., Peronace E., Porchia A., Romagnoli G., Tarquini E. and Moscatelli M.; 2021: Seismic amplifica9on maps of Italy based on site- specific microzona9on dataset and one-dimensional numerical approach . Engineering Geology, Vol. 289, 106170, hbps://doi.org/10.1016/j.enggeo.2021.106170.