Boosting detection of active tectonics with multi-source data and integrated methods: recent outcomes from the Apennines

The Apennine mountain belt is a seismically active region showing coupled extensional- and compressional tectonic regimes. The bulk of the seismic energy is released along the normal-fault systems paralleling the topographic divide where earthquakes with 6.0<7.0 have occurred both in historical- and recent times. Moderately-energetic compressive/transpressive earthquakes (4.0<6.0), which occurred in the last 50 years, are associated instead with recent activity along the outer front of the fold-and-thrust belt. The relatively-low slip rates (1-3 mm/y), peculiar geological settings, fault systems’ immaturity hamper the assessment of Quaternary fault activity, challenging estimation of the seismic hazard. We present the results of multiscale-multidisciplinary approaches carried out in the Sibillini Mts and peri-Adriatic piedmont of Abruzzo and Molise regions, located in the Apennine extensional and compressional domain, respectively. In detail: we investigated the area beyond the northern tip of the Mt Vettore-Mt Bove Fault (VBF), where a remarkable seismicity rate was observed after the 2016 (Mw 6.5) Norcia earthquake. We interpreted primary topographic attributes to direct geological field surveys. We compared (on surface) evidence of distributed deformation with results coming from 3D assessment of fault slip tendency with computation of Coulomb failure function across the potential fault surfaces. We pointed out the seismogenic character of the ∼13 km-long Pievebovigliana master normal Fault (PBF), which strikes N155°E, dips SW and is in right-lateral en echelon setting with respect to the VBF. The reconstructed geometry of the immature PBF is compatible with the occurrence of Mw≥6.0 earthquakes; we addressed the hypothesis of late Quaternary activity along the Apennines Outer Front (SAOF), in central-southern Italy, where compressional tectonics is well documented until the Lower-Middle Pleistocene and the front is buried under Plio-Pleistocene foredeep deposits. By integrating topographic- and fluvial network analyses along with morphotectonic investigation of fluvial terraces we found, in the Abruzzo region, variable evidence of rock uplift along segments of the SAOF and inward structures, on its hanging wall. The observed pattern of anomalies is difficult to explain with long-wavelength regional uplift alone and agrees with the regional seismotectonic framework. Despite the low deformation-rate context challenging the interpretation of the topographic and geomorphic signals, the study suggests a reconsideration of late Quaternary active thrusting in central-southern Italy. Despite the different tectonic contexts, the study areas belong to, and the diversity in scale and resolution of the input data, the integration of different methods of investigation turned out successful while dealing with active tectonics in low-deforming-rate regions. Our results along the Apennines confirm how multidisciplinarity boosts the chance to decipher clues of active tectonics and unveil potentially seismogenic sources.