Geophysical characterization of the shallow subsoil at a heavily urbanized archaeological site: the Roman Amphitheater and the Scrovegni Chapel in Padua.

The characterization of the shallow subsoil at complex archaeological sites requires sufficient spatial coverage and resolution as to provide the necessary information. This is all but trivial, particularly where historical superposition of layers requires also sufficient depth investigation and resolution. The Scrovegni Chapel in Padua, with its Giotto's fourteen century frescoes, and recently added to the list of UNESCO World Heritage Sites, stands on the remains of the local Roman amphitheater. The hypogeum located under the chapel shares its western wall with a part of the wall of the amphitheater. To date, no information is available about the soil below the apse of the chapel. Over the past decade, several ERT and GPR measurements have been conducted outside the chapel, straddling the amphitheater structure for archaeological and geomorphological characterization of the area. In 2021, a first 3D active and passive seismic survey was conducted using about 1500 wireless sensors, aiming at using surface waves to provide a 3D image of the subsurface in terms of shear wave velocity. In 2022 three 20 m deep boreholes were drilled around the chapel and equipped with fiber optics, ground deformation sensors, and electrodes for cross-hole ERT, and about 200 1-C and 3-C wireless seismic sensors were placed around the drilling area. During the drilling, additional 3D seismic data were acquired from the surface, which completed the datasets acquired in 2021. The geophysical data thus acquired and the time-lapse monitoring that will be possible around the area of the Scrovegni Chapel in Padua will allow reconstructing the geomorphology of the subsurface on which the chapel rests, but also to better study and analyze the possible interactions between the structure of the chapel and the buried structure of the Roman amphitheater from the mechanical point of view as well as from the perspective of the seismic response of this specific site.