Engineering-geological modeling for supporting local seismic response studies. Insights from the 3D model of the subsoil of Rieti (Italy)

A high-resolution 3D engineering-geological model of the subsoil can be derived by integrating stratigraphic and geophysical data in order to represent reliably the geological setting, and therefore support several geological studies such as local seismic response analyses. In this study, we show how an accurate 3D engineering-geological model suggests the proper seismic response modeling approach (1D or 2D) in a peculiar and complex geological context, such as the historical city center of Rieti (Italy), selected as test site, and characterized by important lateral heterogeneities between stiff travertine and alluvial soft deposits. The proposed methodology involves three steps: (i) conceptual geological modelling, obtained from data and maps of literature; (ii) engineering-geological modeling, validated through geophysical data; and (iii) a 3D model restitution achieved by a geodatabase (built basing on the previous steps), that collects, stores, reliably represents, and integrates properly the geospatial data. The analysis of seismic ambient noise measurements specifically available for the study area allowed to infer the shear wave velocity value for each lithotecnical unit and to retrieve some additional stratigraphies. These synthetic log stratigraphies allowed to improve the detail of the geodatabase and therefore a more accurate 3D geological model. Such a reliable engineering-geological model of the subsoil is required to perform a site-specific seismic response characterization which is a fundamental tool in the framework of seismic risk management.