GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 - POSTER GNGTS 2023 Figure 1. Geology of the southern-central Crati Basin. The red line indicates the half-Graben master fault (MFF; San Marco Argentano-San Fili Fault). Mod. from Spina et al., 2009. Despite the hanging-wall of MFF matches the highest intensity datapoints of the southward-migrating-sequence of the 1767-1835-1854-1870, Mw~6 earthquakes, the entire Crati basin lacks of both Late Pleistocene-Holocene faulted deposits and/or cumulated surface rupture evidence (Galli & Bosi, 2003; Galli et al., 2007). If true, this fact would imply that the slip-rates of these faults probably decreased since the Middle-Late Pleistocene, hindering surface faulting phenomena in later periods. In order to resolve this ambiguity, in the lack of faulted late Pleistocene deposits, we have tried an opposite approach, i.e., to find out Quaternary deposits sealing the MFF. Field evidence Following 1:33,000 scale aerial-stereo photos investigations, 1-m, LiDAR-derived DTM analyses, and field survey along the whole master fault, we identified a rare case where a geomorphological feature interfered with the fault path. This is a flat, east-dipping surface, capping a 40-60 m thick alluvial fan remnant, made by faintly layered-to-massive heterometric gravels. This surface outcrops south of San Benedetto Ullano (Piano de Rossi) between 600-450 m a.s.l., and it is literally suspended above the surrounding landscape (Fig. 2). It matches a patch of a paleosurfaces that Robustelli and Muto (2017) classified as 2nd order depositional paleosurfaces, datable between the Lower and Middle Pleistocene.