Geophysical investigations on hypogeic monuments. The case study of the Crypt of St. Sebastian in Sternatia (Lecce - Southern Italy).

In this paper, GPR data gathered by the non-destructive investigation campaign, performed by means of geophysical surveys carried out on the vault and the inner pillar of the Crypt of San Sebastiano are shown. The study is part of a wide preliminary diagnostic campaign aimed at the restoration of the monument, which included a thermographic relief on the painted walls and on the vault, a monitoring of climatic parameters such as temperature and relative humidity of the air and of the wall surfaces. In addition, in order to identify the materials constituting the wall paintings and their alteration products, a complex microdestructive diagnostic plane were also performed on micro samples taken from . The gathered GPR data allowed us to identify the anomalies of the calcarenitic mass in order to highlight structural problems that could affect the stability of the monument. To this regard, a different behavior, in terms of homogeneity, alteration and microfracturing of rocky mass has been highlighted for the voult and the pillar of the crypt.