Gravity and GPR modeling of the subsurface structures below the Basilica dello Spirito Santo in Naples (Italy)

This study aims at the interpretation and modeling of the subsurface anthropic structures below the Basilica dello Spirito Santo  in Naples (Italy) through the acquisition and processing of microgravimetric and GPR data. The analysis of GPR data provides significant information about buried elements and architectural stratifications, compatible with interventions from the past. In particular, several cavities were identified and interpreted as graves. However, this method did not image clearly the presence of the church foundation. In addition, we computed the vertical gradient of the gravity data in order to enhance the contributions due to subsurface structures. We then performed a multiscale imaging (multiridge method)  to estimate the depth and geometry of the sources. This analysis revealed that at a depth of about 0.5-1 m, there are several cavities, tombs, shafts, in agreement with GPR data. Most importantly, we also detected at about 5 m depth a rectangular structure that can be interpreted as the church foundation.

Our results demonstrate that the combination of GPR and gravity surveys is a successful strategy to detect subsurface anthropogenic structures in urban areas. In particular, the gravity method proved to be more effective to infer information about the deep church foundations which were questioned, while simultaneously detecting the subsurface cavities that can be attributed to tombs.