Empirical estimates of Site Amplification Factors in Italy

In the framework of an Italian research project (2022-25 PRIN SERENA “Mapping Seismic Site Effects at Regional and National Scale”, granted by the Italian Ministry of University and Research), we aimed at the empirical verification and calibration of the numerical ground-motion amplification maps developed within the project, using in-depth geological, geophysical and seismological information. For this purpose, a database of experimental site-specific amplification estimates (AFs) in three interval periods was created for more than 1900 sites, both at national scale (permanent and temporary seismic networks) and for selected areas (Central Italy, North-East Italy, Basilicata region, Ferrara).

Three different approaches were used to compute the AFs: i) spectrum-compatible accelerograms (Uniform Hazard Spectrum) as input and amplification function from Generalized Inversion Technique (GIT) applied to input motion (Fourier spectrum, FAS, or Response spectrum, SA); ii) estimate based on the repeatable site-to-site terms of a reference Ground Motion Model in SA for the EC8-A class; iii) both input and output computed from recordings at the reference station and at the target one (SSR). A GIS architecture was developed for storage and to perform semi-automatic comparisons between experimental estimates themselves and with the numerical ones using JupyterLab (web-based interactive development environment).

The comparison of AFs from different techniques highlights that experimental estimates are well-correlated in the investigated areas, with better agreement between integral parameters (FA), and that the observed differences with the GIT or SSR estimates are due to the dependence on the reference site and on the choice of earthquake catalogue.