GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.2 GNGTS 2024 The 3D frst arrival traveltme tomography (Heincke et al. 2006) included the picking of the frst breaks for all 3D gathers and inversion through the sofware GEOGIGA (Technology Corp.). Some preliminary analysis was needed in order to fnd the optmum parameters for inversion, including the generaton of synthetc 2D and pseudo 3D models. Picking of frst break tmes for the real 3D dataset was done manually and revealed the most tme-consuming processing step, due to the high level of urban noise pollutng the data. Fig. 1 – Acquisiton scheme for the dense 3D seismic survey. 1C and 3D seismic nodes are represented as blue and yellow triangles, respectvely, while actve source locatons are represented as red stars. The phase velocity maps, the autospectrum gradient maps and the 3D Vp model from frst arrival traveltme tomography reveal the same velocity anomalies, corresponding to known archaeological features such as the walls of the Roman amphitheatre and probable reinforced concrete structures built during the Second World War in order to protect the chapel. A low- velocity area in the south-western side of the study area, already mapped in Barone et al. 2022 and Barone et al. 2023, is clearly visible. Finally, a high-velocity area in the eastern side is also imaged, whose origin is uncertain and that will need further investgatons. In conclusion, this study demonstrates that a combined surface wave and refracton analysis using dense 3D seismic data can be helpful for archaeological prospecton. Despite the noisy urban context, the limited number of sensors (with respect to our previous studies) and the non- optmum geophone spacing, especially for surface wave analysis, a spatal resoluton of a few