High resolution seismic reflection methods to detect near surface tuff-cavities: A case study in the Neapolitan area, Italy

The Neapolitan region of Italy is plagued by the presence of shallow manmade cavities in lithoid tuffs that cause problems for communities because they produce building damages and loss of human lives. A high resolution P-wave seismic-reflection technique was successfully used to define a cavity 6 m by 10 m in horizontal dimensions and with a height of about 6 m located in a tuff layer 10 to 19 m below ground level. Such a cavity was located at Afragola (near Naples) where the local geology is typical of the Neapolitan area. The seismic dataset was acquired by using end-on spread geometry, with 0.25 m spacing for shots and 0.5 m for receivers. The application of band-pass filtering (30-150 Hz) allowed us to remove incoherent noise from the data, while an additional equivalent slope (Vs-1) of 0.005 s m-1 cut in the FK transform results in ground-roll noise removal. Both the acquisition and processing methods have been necessary to investigate and define the shape and dimensions of the targeted cavity.