GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 2.2 GNGTS 2024 Local seismic effects forecast supporHng risk miHgaHon in the Ferrara area. L. Minarelli 1 , M. Stefani 2 , S. Amoroso 3-1 , G. Tarabusi 1 1 Is9tuto Nazionale di Geofisica e Vulcanologia, Italy 2 University of Ferrara, Italy 3 University of Chie9-Pescara, Italy IntroducHon The history of Ferrara has been marked by many significant earthquakes, documented since 1117 (Guidoboni 1984; LocaC et al. 2016; Guidoboni et al. 2018 and Guidoboni et al. 2019). The worst documented damage occurred during the 1570 earthquakes. The seismic acCvity was generated by reverse and, someCmes, strike-slip faults of the Apennines chain front, buried under thick Plio-Pleistocene foredeep deposits. The damage to the anthropic structures was modulated by local seismic effects, reflecCng the complex straCgraphical, geophysical, and geotechnical features of the area. The subsurface architecture induced seismic wave amplificaCon and, at sites, coseismic liquefacCon of water-saturated granular sediments, as occurred in the urban area of Ferrara during the 1570 earthquakes (Guidoboni and Valensise 2023), and in adjacent areas in the year 2012 (Minarelli et al. 2022). For developing the research, over 4,000 pre-exisCng geophysical, straCgraphical, and geotechnical invesCgaCons were collected into a homogeneous database, and analyzed together with the new invesCgaCons we carried out, such as seismic noise measurements, seismic piezocone, and seismic dilatometer tests. Numerical modeling for the seismic response analysis was also performed. Geology and StraHgraphy The distribuCon and properCes of the outcropping fluvial sediments were reconstructed through remote sensing, field invesCgaCon, and geotechnical tesCng. The Po channel sands (Fig. 1a), mainly Medieval in age, form elongated bodies in northern areas, whereas, in southern zones, the Reno channel silty sand and silts accumulated during the XVII century. In south-eastern areas, Roman Times Po and Reno channel bodies are sub-outcropping. The fluvial channel deposits are flanked by finely granular natural levee belts. Most of the study area consists of mainly cohesive, argillaceous sediments, accumulated into interfluvial semngs (Fig. 1a). The conceptual correlaCon of the abundant cone penetraCons tests and straCgraphic cores generated a subsurface geological model, developed throughout the wide Ferrara Municipality area, integrated, in the urban and peri-urban zone, by a lithostraCgraphy 3D model, produced by automated interpolaCon techniques. To generate the model, syntheCc lithological columns were derived from the comparison of the Cp resistance and lateral fricCon values, interpreted according to the Roberston classes (Robertson 1990, 2009). The syntheCc lithological logs and the actual straCgraphic cores were then laterally correlated, using trilinear and tricubic interpolaCon algorithms, to generate conCnuous 3D subsoil models of the first 40 m of subsurface (Fig. 1b, c).