Characterizing the Distributed Faulting During the 30 October 2016, Central Italy Earthquake: A Reference for Fault Displacement Hazard Assessment

Moderate to strong earthquakes (i.e., Mw > ~6.0) commonly produce a complex network of ground ruptures, which are responsible for significant damage. Distributed faulting can affect wide areas (tenths of square kilometers), and expected displacement can be estimated through a probabilistic approach, considering distance from the primary fault and earthquake magnitude. Other factors may have a role in driving the occurrence of distributed faulting; nevertheless, they are not adequately addressed in the current modeling, due to a sensible lack of information. We study the 30 October 2016, Central Italy earthquake (Mw 6.5), to analyze the spatial pattern and geometric characteristics of distributed faulting. We found that distance from the primary structure, fault geometry, and lithology are key factors controlling the distributed faulting occurrence; the local structural setting (i.e., synthetic versus antithetic normal faults systems and relay zones) drives the spatial distribution of faults and the partitioning of the deformation. We also examine other four events occurred in the Italian Apennines since 1980, confirming that traditional models can underestimate the probability of distributed faulting. We suggest that a purely distance-based probabilistic approach should be integrated using additional parameters derived from earthquake deformation fields or considering the reactivation of preexisting faults.