Geological and morpho-tectonic analysis for defining active fault segmentation: case studies from the central Apennines, Italy

Up to now, the complexity and the uncertainty in defining the extent down-dip and along-strike of active faults led to the elaboration of several methods to establish structure 3D geometry. Therefore, different approaches produce different scenarios of seismogenic rupture for the same active tectonic structure. Here we investigate two active fault systems of the central Apennines of Italy: the Roveto Valley Fault and the Laga Mts. Fault. We specifically aim to the understanding of along-strike segmentation of these tectonic structures to contribute to improve the knowledge of the seismotectonic setting of the central Apennines. Overall, our goal is to make a step forward toward the comprehension of the wide theme of seismogenic fault segmentation.

The main uncertainties regarding the two fault systems are different. In the case of the Roveto Valley Fault, the uncertainty is twofold: 1) the current activity of the fault is debated; according to some authors, fault activity ended during the Middle Pleistocene, whereas others suggest the fault is still active and seismogenic; 2) the extent of the proposed active section of this tectonic structure is not clearly defined, and this is relevant in a seismotectonic perspective. The Laga Mts. fault system is a complex tectonic structure whose activity is well geologically documented for the southern section of the system; moreover, the fault system played a key role in the seismogenic process of the 2016-2017 central Italy earthquake sequence. Some authors interpret the fault as the surface expression of a single large seismogenic source, capable of generating seismic events of Mw ≈ 6.7. Other authors, instead, propose that this system consists in two structurally aligned but kinematically independent faults, the Amatrice and Campotosto faults. Following the 2016-2017 seismic sequence, an important debate is taking place within the scientific community about the definition of 1) the individual seismogenic sources that make up the Laga Mts. fault system and 2) the geometric and kinematic relationship between the fault(s) at surface and its (their) possible prolongation at depth as crustal major seismogenic sources.

Through morphological, morphotectonic and structural analyses we propose segmentation criteria and possible segmentation scenarios for these two structures. These allow us to estimate the maximum coseismic rupture and the maximum magnitude expected from a single seismic event for the investigated fault, improving the seismotectonic knowledge of the central Apennines.