Near-surface geophysics for characterizing complex subsurface settings in historically layered monumental urban areas

Historical urban centres of high cultural and monumental relevance are commonly characterized by complex and highly heterogeneous subsurface settings, resulting from the superposition of natural geological deposits, archaeological layers, and centuries of anthropogenic modifications. In such contexts, limited or fragmented subsurface knowledge may hinder archaeological interpretation and constrain multidisciplinary analyses aimed at urban reconstruction and heritage preservation.

This contribution is framed within the Italian PRIN 2022 project NEW AGE (New Integrated Approach for Seismic Protection and Enhancement of Heritage Buildings on Historic Earthen Deposits) and presents results from non-invasive geophysical investigations conducted at two emblematic monumental sites: the Roman Amphitheatre (Arena) of Verona and the Santa Sofia monumental complex in Benevento, both characterized by prolonged and stratified occupation histories, leading to highly heterogeneous near-surface conditions. The investigations benefited from advanced geophysical instrumentation made available through the IRPAC and ITINERIS research infrastructure (funded through regional and national programs, respectively), supporting enhanced data acquisition capabilities within the project framework.

We propose a multi-scale, multi-method geophysical approach designed to improve the characterization of shallow subsurface conditions in densely built and historically layered urban environments. The investigation strategy combines ground-penetrating radar (GPR), electrical resistivity tomography (ERT), and seismic methods, selected to explore complementary physical properties and depth ranges while accommodating site-specific logistical and conservation constraints.

GPR surveys provided high-resolution imaging of shallow subsurface heterogeneities and anthropogenic features, supporting the identification of archaeological remains and spatial variations within near-surface layers. ERT investigations complemented these results by resolving broader geological structures and deeper resistivity contrasts, allowing reconstruction of subsurface variability at different spatial scales. Seismic measurements contributed additional constraints on subsurface layering and mechanical properties.

The combined interpretation of the different datasets acquired, supported by archaeological and geotechnical information where available, provides a robust and physically consistent reconstruction of the shallow subsurface in complex, historically layered monumental settings. The multi-method geophysical framework enables the identification of stratigraphic heterogeneities, anthropogenic layers, and buried structures, reducing subsurface uncertainty in complex heritage contexts and supporting subsequent geological, archaeological, and engineering analyses.