Characterization of shallow volcanoclastic deposits by turning ray seismic tomography: an application to the Naples urban area

Several bidimensional seismic tomography surveys were carried out in urban areas of the Campi Flegrei and Somma-Vesuvius volcanic districts, Naples, Italy, with the aim of investigating the shallow subsurface and of detecting small-scale variation and heterogeneities within pyroclastic deposits. The method employed in this study is turning ray tomography (TRT). With accurate field acquisition and travel time picking and correct choice of inversion parameters, it was possible to obtain detailed P-wave tomographic models in areas characterized by thick beds of pyroclastic deposits. We were able to identify zones with heterogeneous P-wave velocities caused by the presence of buried paleochannels, or by differential welding and zeolitization in the subsurface of the investigated areas. TRT appears to be a suitable method to investigate deposits for engineering applications, at sites where the bedrock is too deep to be reached by foundations and the overburden is characterized by much heterogeneity. © 2002 Elsevier Science B.V. All rights reserved.