1D stratigraphic modelling vs experimental seismic amplification: can a possible convergence exist? The case of Val d'Agri.

Predicting ground motion at the national scale requires reliable estimates of seismic site response, which are often limited by the availability of detailed geological and geotechnical data. Simplified 1D numerical modelling has been proposed to estimate site amplification factors over wide areas, but its reliability in complex geological settings remains an open issue. The Val d’Agri intermontane basin (Southern Apennines, Italy) was selected as a test site. Experimental amplification factors were estimated at 21 seismic stations using the generalized inversion technique applied to more than 2000 earthquake recordings. These results were compared with 1D stochastic and deterministic modelling. The comparison shows good agreement for sites with shallow sedimentary cover, while significant discrepancies arise for thicker sedimentary sequences and deep basins, where 1D models systematically underestimate the observed amplification. The results highlight the limitations of simplified 1D approaches in complex geological contexts and the importance of experimental data to properly constrain seismic site response.