3D High-resolution seismic tomography on a Tuff Cliff in the Sorrento Peninsula, Italy

This paper shows an example of 3D high-resolution seismic tomography that implements an acquisition geometry, which provides for the housing of sensors in the sub-vertical discontinuities of a tuff cliff. The site test was located in the Sorrento Peninsula, a major Quaternary morphostructural unit of the western flank of Southern Apennines, consisting of a narrow and elevated mountain, that separates two major embayment of the eastern Tyrrhenian margin. The overall geological setting is characterized by a carbonate bedrock, covered by pyroclastic deposits (i.e. "Campania Ignimbrite"), originated from the Campi Flegrei volcanic district. The occurrence of steep slopes and the high relief area, along with the marine erosion at the base of the coastal cliff, creates favorable conditions for the occurrence of a generalized instability of the slopes characterized by tuff rock falls as prevailing landslide phenomena. An accurate prediction of these mass movements is difficult if not accompanied by an intensive hydrogeological and geotechnical monitoring and hazard assessment; the instability phenomena, in fact, can be caused by the presence of pervasive fracturing and cavities in the tuff rock. Due to logistical reasons, it is not possible to perform seismic surveys using typical acquisition setup, therefore we utilized a particular experimental procedure, characterized by an acquisition geometry which included the installation of the sensors on the tuff cliff and energize along concentric semicircles to obtain the maximum of the seismic resolution. A non linear seismic inversion was used to obtain 3D High-resolution seismic tomography in terms of P-wave velocity and S-wave velocity. The interpretation of the experimental results in terms of 3D Vp/Vs ratio showed anomaly zones in the investigated rock. We identified an area with a low Vp/Vs value that we ascribed to a medium porosity or in dry condition with respect to the surrounding rock mass.