Structural complexity and mechanics of a shallow crustal seismogenic source (Vado di Corno Fault Zone, Italy)

The mechanics and seismogenic behaviour of fault zones are strongly influenced by their internal structure. In this perspective, the internal structure of the extensional seismically active Vado di Corno Fault Zone (VCFZ, Central Apennines - Italy) was quantified by combining high-resolution structural mapping with 3D fault network analysis over 2 km along fault strike. The fault zone was exhumed from 2 km depth in carbonate rocks, accommodated 1.5-2 km of extensional throw since Early-Pleistocene and cuts through the Pliocene Omo Morto Thrust Zone (OMTZ) with partial reactivation in extension. The exceptional exposure of the footwall block allowed us to reconstruct in detail the geometry of the OMTZ and quantify the spatial arrangement of master/subsidiary faults and fault zone rocks within the extensional VCFZ. The combination of the structural map and the 3D fault network with kinematic and topological analyses, pointed out the crucial role of the older thrust geometry (i.e. lateral ramps) in controlling the along-strike segmentation and slip distribution of the VCFZ. These observations were discussed in the framework of regional extension through a slip tendency analysis and a simplified mechanical model, which suggest the activation of oblique inherited structures during the lateral propagation of the VCFZ segments. The interaction of the VCFZ with the OMTZ generated along-strike and possibly down-dip mechanical asperities. Considering the exhumed VCFZ as an analogue for the shallow structure of other seismic sources in the Central Apennines, similar settings could play first-order control on the spatio-temporal evolution and rupture heterogeneity of earthquakes in the region.