GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 3.2 444 Conclusions The processing and interpretation of the scans has highlighted that the 600 MHz antenna was more suitable than the 200MHz antenna for this kind of investigations, achieving a better shallower response with higher resolution and an acceptable depth of penetration of about 2.5 m. This study has permitted to identify in the subsurface of San Sebastiano church a series of reflectors of different nature and geometry. The most interesting feature is a barrel vault crypt located in correspondence of the nave with a square section and side of around 2.8-3.0 m. The decking of the crypt is at approximately 1.5 m below the superficial church floor. Figure 3a shows a transverse section of the church with the radargram of TPV_9 profile. In the scan is visible and well bounded the extension of the crypt and its geometry, with the typical barrel vault. Due to the collapse of the pavement before the GPR survey, a first crypt with remains of human skeletons was discovered in the beside structure of the church. Therefore, it is reasonable that the crypt identified with the GPR was similarly used as mass grave of burial. Have also been identified some smaller reflectors with different shapes and dimensions, divided in two categories: • Point reflectors which are likely structural associated; these are characterized by high amplitude related with a strong dielectric contrast and are possibly caused by small elements such as single graves, buried walls or old foundations. • Point reflectors which are likely lithological associated; these are lower amplitude reflectors generally horizontal or with a slight slope, possibly related with subsurface conditions such as small cavities, lithological variations between fill material and bedrock or variations inside the fill material. In the apse and in the adjacent structure it was noticed a high dampness of the subsurface, probably because of a thicker or different particle size of the fill material. In the external area no significant reflectors have been identified, except for a small isolated feature of generic nature behind the apse. The use of the GPR technique has allowed to obtain fundamental information about anthropic structures in the church subsurface, in particular crypts used like mass grave burial considering the high number of human skeletons. References Barilaro, D., Branca, C., Gresta, S., Imposa, S., Leone, A., Majolino, D.; 2007: Ground penetrating radar (GPR) surveys applied to the research of crypts in San Sebastiano’s church in Catania (Sicily) . Journal of Cultural Heritage, 8(1), 73-76. Carbone, S., Lentini, F., Branca, S.; 2010: Note illustrative della Carta Geologica d’Italia a scala 1:50000 - Foglio 633 Paternò . ISPRA, Servizio Geologico d’Italia, 160 pagg., 44 figg., 11 tabb., Roma. Davis J.L., Annan A.P.; 1989: Ground-penetrating radar for high-resolution mapping of soil and rock stratigraphy . Geophysical Prospecting, 37, 531-551. Forte E. and Pipan, M.; 2008: Integrated seismic tomography and ground-penetrating radar GPR for the highresolution study of burial mounds tumuli. Journal of Archaeological Science , 359, 2614-2623. Goodman D. and Piro S.; 2013: GPR Remote Sensing in Archaeology . Springer Berlin Heidelberg. Grassi, S., Imposa, S., Patti, G., Boso, D., Lombardo, G., Panzera, F.; 2019: Geophysical surveys for the dynamic characterization of a cultural heritage building and its subsoil: The S. Michele Arcangelo Church (Acireale, eastern Sicily) . Journal of Cultural Heritage, 36, 72-84. IDS Ingegneria Dei sistemi S.p.A.; 2009: Software Gred elaborazione dati Georadar Imposa, S., Mele, G.; 2011: Ground penetrating radar survey inside the S. Agata cathedral of Catania (eastern Sicily) . International Journal of Architectural Heritage, 5(2), 188-197. Imposa, S., Grassi, S.; 2015: Georadar survey inside the Santa Maria Maggiore church of Ispica (Sicily- Italy). Environmental Earth Sciences, 73(5), 1939-1949.