Interseismic locking vs. aseismic slip of carbonate–hosted normal faults: Insights from the northern Apennines, Italy

Carbonate–bearing terrains represent important loci of earthquake nucleation and propagation in the shallow seismogenic crust; therefore, understanding fault mechanical behavior is fundamental in these rocks. Current models of fault slip mode generally assume: (1) slow/stable creep and fast/unstable slip to be separated in space and to occur in different fault patches, (2) aseismic sliding to be restricted to lithology–controlled weak domains, and (3) rate–weakening patches to be interseismically locked. We believe this view suffers from some physical and conceptual limitations when considering the available geological and geodetic data. We study three exhumed carbonate–hosted upper–crustal normal faults of the northern Apennines (Italy) by combining (micro)structural analysis with geodetic data and fault mechanics considerations. We bring evidence across a range of spatial scales, suggesting mutually overprinting seismic and aseismic slip along the same fault patches in phyllosilicate–poor limestone at different phases during the seismic cycle. We assess the hypothesis that carbonate–hosted normal faults at upper–crustal conditions may undergo interseismic creep dominantly by cataclastic flow and plastic deformation. We think our work provides new insights into the fault slip modes in carbonate terrains and may impact future studies on seismogenic potential and earthquake hazard assessment.