GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 The November 9, 2022, compressional seismic sequence (Mw 5.5)- another piece of information to the 3D seismotectonic fault model of the Marche-Adriatic offshore area (Italy) R. de Nardis 1-2 , F. Pietrolungo 1-2 , C. Pandolfi 1-2 , S. Bello 1-2 , D. Talone 1-2 , G. Lavecchia 1-2 1 DiSPuTer, University “G. d’Annunzio”, Chieti, Italy 2 CRUST - Centro inteRUniversitario per l’analisi SismoTettonica tridimensionale, Italy Besides the Southern Alps compression in Italy, active contraction is observed along the Apennine Outer Thrust System (OTS) of the Apennine-Maghrebides fold and thrust belt. Two major outward convex arcs characterize it, the NNE-to-ENE verging northern Padan-Adriatic arc and the SE-to-S verging southern Ionian-Sicilian arc, linked by a linear segment in southern Apennine. The OTS is buried in the Padan Plain and extends offshore in eastern and southern Italy. This peculiarity, jointly with a spread minor- to - moderate seismic activity (ISIDe Working group, 2007; Cattaneo et al., 2019) and a complex multi-depth deformation pattern, makes the Italian Quaternary compressional domain a topic of scientific debate among the seismotectonic community (Boncio and Bracone, 2009; Vannoli et al., 2004, Mazzoli et al., 2014, Ferrarini et al., 2021, Jenny et al., 2006; Lavecchia et al., 2003; Visini et al., 2009; Petricca et al., 2019). The coastal Marche-Adriatic region of eastern-Central Italy has especially been questioned in the literature regarding its activity, seismogenic potential, and stress regime type, e.g., compressional or strike-slip. High-quality seismological data from a local network integrated with long-term geological constraints allowed us to build a 3D crust-scale seismotectonic fault model (de Nardis et al., 2022 and references therein). Late Pliocene-to-Quaternary NE-verging fold-and-thrust structures develop at the hangingwall of the Adriatic Basal Thrust (ABT), an SW-dipping reverse shear zones which penetrate across the entire crust and is seismogenic at upper and lower crust depths. The November 9, 2022, seismic sequence activated one offshore ABT upper crustal splay with pure compressional kinematics (Fig.1). Two major events (Mw 5.5 and 5.2) were enucleated within 1 minute at depths of ~5 km and ~7.5 km, respectively, and ~8 km away in map view. At a depth of a few kilometers, the seismogenic thrust intercepts two deep extraction wells (Pesaro Mare 4 and Bice 1). Geological section, hypocentral cross-sections, focal mechanisms, and available