The latter is the result of multi-ple phases of deformation, from the Early Jurassic, during the rift phase, which led to the opening of the Tethyan Ocean, to compression in Neogene, linked with the evolution of the Apennines fold and thrust belt.
The Montagna dei Fiori has received attention by geologists through the past decades because of both its Jurassic stratigraphy and its complex present-day structure. More in general, the 4-D high-resolution image of a crustal volume hosting an active linkage zone between two large seismogenic structures provides new insights into the behavior of interacting faults in the incipient stages of connection. This also generates substantial issues with earthquake geological studies carried out prior to the recent seismic events in central Italy. Therefore, the evaluation of the seismic hazard in the Campotosto area should not be based on the geometrical characteristics of the outcropping MGF. However, the geological evidence provided with this study suggests that the MGF is of early (i.e., pre- to syn-thrusting) origin. Mainly due to its geomorphologic expression, this fault has been considered as an active and silent structure (therefore representing a seismic gap) able to generate an earthquake of Mw max = 6.5−7.0. This has important implications for seismic hazard assessment in an area dominated by the occurrence of a major NW-SE−striking extensional structure, i.e., the Monte Gorzano Fault (MGF). Based on the underlap dimension, the seismogenic potential of the CSZ is in the order of Mw = 6.0, even in the case that all the faults belonging to the zone were activated simultaneously. In this paper, the seismogenic faults related to the main seismic events that occurred in the Campotosto Seismic Zone (CSZ) were modeled and interpreted as a linkage fault zone between the PF and MVF interacting seismogenic faults.
This latter was affected by seismic swarms with magnitude ranging from 5.0 to 5.5 during the 2009 seismic sequence and then in 2017 (i.e., a few months later than the mainshocks related with the 2016 seismic sequence). The seismogenic faults responsible for the 2009-L′Aquila Mw = 6.3 (Paganica Fault-PF) and 2016-Amatrice-Visso-Norcia Mw max = 6.5 (Monte Vettore Fault-MVF) are right-stepping with a negative overlap (i.e., underlap) located at the surface in the Campotosto area. These seismic events were caused by two NW-SE−striking, SW-dipping, seismogenic normal faults that were modeled based on the available focal mechanisms and the seismic moment computed during the relative mainshocks. In the last decade central Italy was struck by devastating seismic sequences resulting in hundreds of casualties (i.e., 2009-L′Aquila moment magnitude = 6.3, and 2016-Amatrice-Visso-Norcia Mw max = 6.5). Foreland extension is consistent with existing geodynamic models for the Apennines, and could represent the effects of lithospheric bending: its recognition and documentation elsewhere could provide significant insights to improve our understanding of syn-orogenic basin dynamics. Extensional deformations are systematically found within sequentially younger Tortonian, Messinian and Early Pliocene foredeep basins, thus suggesting that normal fault development was an intrinsic feature of the evolving belt-foredeep-foreland system. New surface data integrated with available seismic reflection profiles across the Central Apennines of Italy reveal the occurrence normal faults located in the inner edges of foredeep depressions. Normal faults at the beltforedeep boundaries, by contrast, are far less documented, nor their occurrence is predicted by simple orogenic load models. Extensional deformations are common within foredeep basins, and generally consist of hinterland-dipping normal faults located at the foredeep-foreland transition zones.