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

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 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 iden-
tifying 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 reflec-
tivity 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.