The Vallo di Diano Fault System: New Evidence for an Active Range-Bounding Fault in Southern Italy Using Shallow, High-Resolution Seismic Profiling

摘要

Range-bounding normal faults can present significant challenges for seismic exploration. This is the case of the fault system bounding the Vallo di Diano, the largest intermountain basin in the southern Apennines seismic belt. Industry reflection profiles define the large-scale structure of the basin but barely image the shallow fault system due to unfavorable topographic and near-surface conditions along the foothills of the eastern range. We present two high-resolution (HR) wide-aperture profiles recorded at the eastern margin of the basin across unreported scarps that affect Middle-Late Pleistocene alluvial fans and slope debris. The survey is aimed at identifying possible recent faulting across these challenging terrains and at understanding the relationship between shallow structures and the master range-bounding fault at depth. Common depth point processing of wide-aperture reflection data and first-arrival travel-time tomography provide detailed images of the upper 200-300 m and sounding evidence of recent activity along previously unknown splays of the fault system. These splays dissect the Mesozoic limestone bedrock and alluvial-fan sequences, affecting their depositional pattern. Very high resolution V-P and reflectivity images also give hints of possible coseismic surface faulting in Holocene colluvia. These results have relevant implications for the evaluation of the seismogenic potential of the range-bounding fault system and for seismic hazard assessment of the densely urbanized Vallo di Diano basin.