Combined GPR and ERT prospecting for non-invasive investigation of the Roman Amphitheater in Verona (Italy) and its surroundings

The Italian NEW AGE project (PRIN 2022 “New Integrated Approach for Seismic Protection and Enhancement of Heritage Buildings on Historic Earthen Deposits”) seeks to advance seismic risk mitigation strategies for all cities with significant monumental heritage and all historic centres.

The project adopts a holistic approach, treating the urban environment as an integrated soil-building system, to assess and address the mutual interactions between subsurface conditions and overlying cultural heritage structures. This approach is crucial for the effective preservation of heritage sites in seismic-prone areas.

Seismic investigations, integrated with electromagnetic (GPR) and electrical resistivity tomographies (ERTs), provide non-invasive methods suitable for investigating subsurface conditions and foundation structures beneath urban environments. GPR is particularly effective for characterizing  the shallower layers of subsoil and for detecting possible buried archaeological features. Similarly, ERT is a robust and cost-effective method for delineating the geometry of geological structures in urban areas, at greater depths.

The project employs a multiscale, multiresolution geophysical strategy to comprehensively study the geological subsurface, soil-foundation systems, and heritage structures. By integrating these methods, the PRIN NEW AGE project aims to provide a robust framework for seismic risk mitigation and the sustainable preservation of cultural heritage in urban areas. The proposed strategy was tested to characterize the subsurface of the Arena di Verona from an archaeological and geological point of view, through the combined and integrated use of Seismic, GPR and ERT. In this presentation, only the results obtained with GPR and ERT will be presented while the seismic analyses will be presented by Gallipoli et al. in the work “Rapid and non-invasive structural characterization of the Roman Arena in Verona, Italy, through geophysical prospecting”. 

GPR acquisitions were performed with a monochannel system coupled to antennae operating at different frequencies, and a multichannel GPR stepped-frequency system equipped with an external GNSS system.  GPR data collected by the first GPR system, operating at frequencies of 200 and 400 MHz, allowed the identification of the Arena foundation system, while the multichannel system, leveraging the unmatched resolution offered, enabled the identification of interesting anomalies within the amphitheatre and surrounding areas, belonging to different historical phases.

ERTs  were carried inside the Arena and in Piazza Bra. In Piazza Bra, two ERTs were conducted with a 5-meter electrode spacing, covering a total length of 235 meters, to investigate depths of up to several tens of meters for geological purposes while, in the Cavea, two ERTs  were conducted in two different arcades, along with a roll-along ERT survey in the longitudinal tunnel beneath the Cavea for improving the resolution and supporting the archaeological research.

The information obtained with GPR and ERTs, supported and validated by archaeological data and geotechnical drilling have provided highly valuable insights from both the engineering and the archaeological perspectives.

Geophysical activities are realized also exploiting instrumentations and facilities provided by the Research Infrastructures of IRPAC (financed by PO FESR Basilicata 2014-2020 – DGR n. 402 del 28.06.2019 / CUP: G29J19001190003) and ITINERIS (financed by European Union – Next Generation EU, PNRR, M4C2 inv.3.1, CUP B53C2200215000).