GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 Figure 1. Shaded relief map of the region traversed by the Norcia fault system (blue lines, NFS. CPF, Campi-Preci faults; NF, Norcia fault; MAF, Mount Alvagnano faults; CF, Cascia faults) and by the Mount Vettore (black, MVFS). Yellow circles, macroseismic epicenters of Mw ≥ 5.5 earthquakes (mod. from CPTI15, 2015). 1-6 diggers are the paleoseismological sites presented here. Results from Norcia-Nottoria segment This 10-km-long fault (NF in Fig. 1) bounds the Quaternary basin of Norcia, which is filled by alternating Lower-Middle Pleistocene fluvial-lacustrine deposits, and is capped by Late Pleistocene coarse deposits belonging to coalescing alluvial fans. The master fault that downthrows the Meso-Cenozoic bedrock is usually hidden below a huge nail of slope deposits, with the slickenside in the marine carbonate footwall outcropping sparsely mainly along the southern sectors. To the north, a pair of noticeable synthetic and antithetic splays (the latter not shown in Fig. 1) affect the distal portion of the Patino alluvial fan, where the residential buildings of Norcia sprang up in the past decades outside the medieval walls. We dug trenches 11 and 13 (#3 and #2 in Fig. 1) across these secondary splays, enriching the paleoseismic framework depicted by the preceding 10 trenches. The choice of the trenching locations was enlightened by the results obtained in several ERT performed before in different sites. On the other hand, for the first time, we were able to investigate the activity of the master fault, taking advantage of a temporary excavation that unearthed an amazing case study, i.e., an ancient limekiln displaced vertically by 1.1 m while it was still in operation in the 1703 earthquake, as suggested by several AMS datings of charcoals (see details in Galli et al., 2022).