Borehole seismic surveys for the mechanical characterization of a calcarenite cliff in the area of Ispica (southern Sicily)

Abstract

In this study, we investigate the mechanical properties of the substrate underlying the historical Franciscan Friars Minor convent of Ispica (southern Sicily). The convent, where new fractures recently occurred, is located on top of a calcarenite cliff formed along one of the planes of the regional Pozzallo-Ispica-Rosolini normal fault system. Taking advantage of three existing mechanical drillings 30 m deep, we have carried out down-hole tests (DHT) and a seismic tomography survey in up-hole configuration. The down-hole tests provided vertical profiles of P- and S-wave velocity measured at 1-m depth intervals, from which we have derived the basic elasto-dynamic and seismic parameters, while the tomography survey imaged vertical sections of P-wave velocity across the cliff. The results highlight variable mechanical properties of the subsoil and a step-like pattern of velocity variations parallel to the cliff face that could suggest the occurrence of secondary ruptures related to the main Ispica fault.