Three-dimensional geological modelling of the Cassino Basin (central Italy) for seismic risk mitigation in civil and environmental engineering applications

Integrating detailed geological models into civil and environmental engineering projects is fundamental for an informed infrastructure design and an accurate seismic risk assessment, particularly in complex tectonic and hydrogeological settings. This work illustrates the methodological approaches and practical applications for developing a 3D geological model of the Cassino Plain, an intermontane basin of central Italy characterised by a significant seismic hazard and complex hydrogeological conditions. The area is affected by major infrastructures, including the initial part of the Western Campania Aqueduct. The study involves comprehensive geophysical, geological, hydrogeological and geotechnical analyses, combining borehole data, seismic ambient noise measurements, and advanced geostatistical techniques to delineate the bedrock’s morphology and reconstruct a 3D geological reference model. The Cassino Basin, formed during Pliocene- Pleistocene tectonic activity, features a complex horst-and-graben arrangement with varying thicknesses of Quaternary alluvial sediments resting on carbonate and arenaceous bedrock (Saroli et al., 2020). Past seismic events highlight the need for precise identification of the seismic bedrock to evaluate local seismic amplification phenomena effectively. This study integrated 130 boreholes extending to depths down to 350 m b.g.l. and more than 260 seismic ambient noise measurements to create a detailed 3D geometrical model of the bedrock. Seismic ambient noise data, analysed via Horizontal-to-Vertical Spectral Ratio (HVSR), revealed pronounced impedance contrasts and provided precise mapping of resonance frequencies, which correlated very well with the bedrock depth available from borehole data. Advanced geostatistical interpolation was utilised to transform scattered geophysical measurements into a coherent, spatially continuous map. This enabled the identification of the seismic bedrock surface and facilitated the estimation of sediment thickness through empirically derived relationships between resonant frequency and soil thickness (D’Amico et al., 2008; Van Noten et al., 2022). Virtual boreholes have been generated to augment physical subsurface investigations, which, together with real boreholes, significantly enhanced the resolution and reliability of the 3D geological reference model of the basin. Available boreholes were further exploited to classify the Quaternary filling below the city centre, defining at least four lithological layers, characterised by specific geotechnical properties, and two different aquifers: a shallow multi-level hydrostratigraphic aquifer and a deep pressurised aquifer. The integrated model supports civil engineering by enhancing site-specific seismic hazard assessment, soil-structure interaction analysis, and infrastructure resilience. It proves the value of multidisciplinary geological modelling in reducing uncertainties and seismic risk in complex settings.