Site and building characterization of the Orvieto Cathedral (Umbria, Central Italy) by electrical resistivity tomography and single-station ambient vibration measurements

A multidisciplinary approach based on the integration of geological and in situ geophysical techniques was applied to investigate the Orvieto Cathedral (Umbria, Central Italy) and the underlying subsurface. Notwithstanding this Cathedral has successfully survived different earthquakes occurred in the region, it shows some signs of damage that arise uncertainties about its safety under future seismic events. In order to investigate its unknown foundation geometry, to reconstruct the geological setting and to characterize from a static and dynamic point of view the site-structure system, geological investigations together with electrical resistivity tomography and horizontal-to-vertical spectral ratio analysis of single-station ambient vibration recordings were carried out. The exploitation of these two different geophysical techniques allowed us (1) to delineate the unknown foundation geometry of the Orvieto Cathedral, (2) to estimate the main resonance frequencies of the Cathedral and (3) of the Orvieto site, and (4) to retrieve information about its deep subsurface engineering-geological structure.