Coulomb stress transfer between parallel faults. The case of Norcia and Mt Vettore normal faults (Italy, 2016 Mw 6.6 earthquake).

We investigated Coulomb stress transfer (CST) between the two normal, parallel nearest-neighbour seismogenic Monte Vettore and Norcia Faults (central Italian Apennines). Soon after the Mount Vettore Fault System earthquake of 30 October 2016 (Mw 6.6), we surveyed surface faulting evidence along both this and the Norcia Fault System, wondering on the mechanism that could have triggered the discontinuos surface ruptures formed along the latter. Really, seismological data show that the Norcia Fault did not release earthquakes during the 2016–2017 central Italy seismic, i.e., did not slip at depth. First, we mapped and defined the coseismic slip vector of the surface coseismic ruptures. Geological-structural data and geological cross-sections have been integrated to identify kinematic constraints and the relationships between the two faults systems. Then, we calculated the Coulomb stress generated by the Monte Vettore Fault System on 30 October. Results show that a positive lobe formed in the uppermost volume of the hanging-wall of the Norcia Fault System. Then, we simulated the Coulomb Stress Transfer in the case of the activation of the Norcia Fault System. From our analyses, it is possible to hypothesize that during a high magnitude seismic event (Mw 6.6–6.9) these two parallel fault systems can interact by transferring Coulomb stress reciprocally, although at different crustal level, and with different implications.