Fault Rheology Control on Rupture Propagation and Aftershocks Distribution during the 2016–2017 Central Italy Earthquakes

The stress released by large coseismic ruptures and related aftershock sequences is a strongly
heterogeneous process. We show highly resolved images of the normal fault system ruptured during
the 2016-2017 Central Italy earthquake sequence, as obtained by high resolution local earthquake
tomography allowing relocation of a massive set of aftershocks. We get evidence that lateral changes
of elastic properties on the fault planes account for the complexity in the rupture processes during the
two M>6 earthquakes. We observe an emergent phase in the first part of the Mw6.5 rupture and the
coseismic slip becomes large when the rupture breaks through high Poisson ratio portions of the fault.
Mainshocks break fault portions that, although limited and segmented by inherited structural
complexity, were dynamically interfering during the faulting episodes. The close repetition of slip on
the same relatively high Poisson ratio patch suggests a dynamic weakening of the fault and/or an
incomplete stress release during the first mainshock.