The segmented Campo Felice normal faults. Seismic potential appraisal by application of empirical relationships between rupture length and earthquake magnitude in the central Apennines, Italy

During earthquakes, fault rupture can involve multiple segments in synchronous or cascade mechanisms, leading to an increasing magnitude of the mainshock or rate of aftershocks. Since the seismogenic portions of faults are inaccessible, studying the geometrical and mechanical interaction between exhumed fault segments can contribute to the understanding of multisegment and cascade earthquake scenarios at depth. We investigated a segmented active normal fault system in the Campo Felice area (central Italian Apennines), where fault scarps are well exposed. In this area, there are no instrumental-historical records of intermediate-strong earthquakes, although paleoseismology provided evidence for ancient Mw > 5 earthquakes. Geometry and kinematics of the studied faults as well as their physical linkage and mechanical interaction were assessed. Results of field surveys and geological-structural mapping, serial cross-sections, and throw versus distance diagrams highlight different stages of mechanical interaction between the Campo Felice faults. The suitability of three empirical equations relating earthquake rupture length and magnitude was tested in comparison to a new equation that we developed considering the last seven Mw > 5.5 earthquakes (1997–2016) from the central Apennines. Results show that the Campo Felice faults can produce earthquakes with maximum Mw of ∼5.8 and 6.2 with single or synchronous ruptures, respectively. In turn, Coulomb stress change modeling shows that the seismic hazard can increase considering a quasi-synchronous or cascade activation of the Campo Felice faults together with nearby faults.