High-Resolution GPR Surveys to Investigate the Internal Structure of Pillars Inside the Cathedral of San Giorgio in Ragusa Ibla

Abstract

The Cathedral of San Giorgio, a chief example of Baroque architecture in Sicily (Italy), has been the focus of extensive geophysical investigations aimed at structural and subsoil characterization to support heritage conservation efforts. This study is among the few to apply a high-resolution Ground Penetrating Radar (GPR) survey to the pillars of a Baroque Church, revealing internal structural details not documented in any available historical sources. Using a 2 GHz antenna, parallel radar profiles, spaced 0.05 m apart in both directions, were collected to reconstruct a detailed 3D model of the internal structure. Depth-slice and 3D-view analyses revealed multiple reflector sets corresponding to the different masonry blocks forming the pillars. Distinct internal layers were identified at depths of 0.22–0.30 m and 0.40–0.55 m, indicating blocks approximately 0.20–0.30 m in height and the possible presence of vertical connectors. These results complement previous studies that defined the dynamic parameters of the structure and a 3D velocity model of the subsoil, which suggested anomalies linked to remnants of the ancient Byzantine church of San Nicola. Overall, the findings provide valuable insights into the construction techniques and current condition of the pillars, contributing essential data for the planning of conservation and restoration strategies.