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 man-made 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.