Fault Planes, Fault Zone Structure and Detachment Fragmentation Resolved With High-Precision Aftershock Locations of the 2016–2017 Central Italy Sequence

Three devastating earthquakes of M_W ≥ 5.9 activated a complex system of high-angle normal, antithetic, and sub-horizontal detachment faults during the 2016–2017 central Italy seismic sequence. Waveform cross-correlation based double-difference location of nearly 400,000 aftershocks illuminate complex, fine-scale structures of interacting fault zones. The Mt. Vettore–Mt. Bove (VB) normal fault exhibits wide and complex damage zones, including a system of bookshelf faults that intersects the detachment zone. In the Laga domain, a comparatively narrow, shallow dipping segment of the deep Mt. Gorzano fault progressively ruptures through the detachment zone in four subsequent M_W ∼ 5.4 events. Reconstructed fault planes show that the detachment zone is fragmented in four sub-horizontal, partly overlaying shear planes that correlated with the extent of the mainshock ruptures. We find a new, deep reaching seismic barrier that coincides with a bend in the VB fault and may play a role in controlling rupture evolution.