GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.2 - POSTER GNGTS 2023 Fig. 1 (a) The Italian peninsula with the Umbria region (light yellow polygon), the red dot locates the NUB. (b) Geological Map of the NVU with major historical earthquake epicenters (orange squares with dates and magnitudo equivalent). Red lines are the principal extensional fault outcropping in the area. Valle Umbra Geology The NVU is an NNW-SSE 20 km long and 10 km wide and flat valley located west of the “inner ridge” of the Northern-Central Italian Apennines (Fig 1). The intermontane depression formed in response to the extensional tectonics dissecting the pre-existing fold-and-thrust belt system during the Quaternary period. The Plio-Pleistocene continental sequence infilling the NVU consists of a complex succession of laterally discontinuous deposits, mainly composed of lignitiferous clays, sands, sandy clays and conglomerates. The alluvial sequence is more than 150-200 m thick (GE.MI.NA , 1962) with lateral variations due to the presence of fluvial conoids and the structural organisation of the underlying bedrock. The continental sequence of the depositional environment is characterised by braided rivers and shallow lakes (Bevagna Unit BU in Fig. 2b, Bucci et al., 2016) outcropping extensively in the South-Eastern limits of the NUB. The Marnoso Arenacea Formation (early to middle Miocene, Mutti, Ricci Lucchi, 1972) and the Cretaceous to Oligocene Umbria–Marche carbonate multilayer of pelagic origin with, at the bottom, the limestones formed in shallow-water platforms in the lower Liassic (Calcare Massiccio