Integrated prospecting in the Crypt of the Basilica of Saint Nicholas in Bari, Italy

Particular environmental condition, the effects of pollution, the weathering and the human negligence cause severe and sometimes irreversible damage to buildings and monuments of cultural interest. It is well known that the presence of water and/or moisture content in a porous material is the initial cause of deterioration. In a building of cultural importance, namely the crypt of St. Nicholas in Bari, Southern Italy, non-destructive integrated geophysical surveys (GPR and Seismic sonic) were undertaken in order to investigate the subsoil. The aim was twofold, namely to investigate both about the consistence of some restoration works performed in 1950 and about the presence of features of archaeological interest. The GPR technique has been exploited also to characterize the subsurface water-content under the crypt. In particular, the existence of underground discontinuities, due to the quoted restoration works, has been identified and examined. Moreover, by means of electromagnetic wave velocity analysis, we obtained a qualitative estimate of the volumetric water-content under the floor of the crypt. The results indicated the main causes of the deterioration in the crypt and provide significant information for the safeguard of this historical building. Furthermore, the GPR survey, also, allowed to locate some features of archaeological interest under the crypt. Finally, both a sonic tomography and a GPR survey performed on the precious mosaic were able to identify the ‘internal’ factors responsible for deterioration.