Geometry and seismic characterization of the subsoil below the Amphitheatrum Flavium, Rome

The seismic-risk assessment of archeological and monumental sites is extraordinarily challenging from the earthquake engineer’s point of view: the monumental structures are generally unconventional and of great value, the geology and ground conditions are often poorly known and the presence of tourists in the area can be massive. In addition, the effects of anthropic and artificial deposits on seismic ground motion are particularly relevant within urban historical sites and should be addressed thoroughly. Under these conditions, non-destructive geophysical methods can be successfully employed to identify key parameters for seismic verification. The main focus of this paper is the application of non-invasive geophysical methods to investigate a famous monumental structure: the Colosseum or Amphiteatrum Flavium (Rome, Italy). Because of the complexity of the subsoil under the Colosseum, a comprehensive 3D approach should be encompassed to fulfil the lack of information still pending on the complex subsoil geometry and characterization, as well on the shape of the monument’s foundations. Our investigations are mostly focused on the southern sector of the monument, basically for budget reasons. Despite these limitations, our findings do however contribute to link the reference geologic model to the specific conditions of the anthropic layer and the seismic bedrock at this site, as well as the foundations and the buried parts of the monument below the former arena, providing key input data for the assessment of the response of the Colosseum under dynamic loading.