Inferring the sub-surface connectivity and structural maturity of the Roccapreturo normal fault system, Central Apeninnes, Italy, using high-resolution structural mapping

Zoe K Mildon , Billy Andrews, francesco iezzi, Marco Mercuri, Joanna Faure Walker, Gerald Roberts, Constanza Rodriguez Piceda

Constraining how active faults link together in the sub-surface and understanding how fault geometry and structural maturity affect earthquake propagation are key tools for understanding earthquake behaviour and seismic hazard. We use the Roccapreturo fault system, from the Central Apennines, Italy, which has three closely spaced normal faults mapped at the surface as a case study to explore these questions. Here we present a high-spatial-resolution database of structural (strike/dip) and kinematic (trend/plunge of slip vectors) measurements, as well as Holocene and geological throw measurements. We find that the fault geometry is highly variable, with strike ranging from 072° – 183°, dip varying from 42 – 82°, and the fault trace is variably segmented along-strike. Steeper fault dips occur within a relay zone between two strands. We interpret this observation as supporting evidence that these fault strands are connected in the sub-surface. Twelve Holocene throw profiles and seven geological cross-sections were collected, the maximum Holocene throw is 8.75 ± 1.75 m (giving a Holocene-averaged throw rate of 0.58 ± 0.16 mm/yr) and the maximum geological throw is 610 m (giving a T/L ratio of 0.055). Strain rate calculations, using the high-resolution structural, kinematic and Holocene throw data, show a smooth variation in the strain rate of the fault, despite complex surface geometry, implying that the fault geometry and slip are coupled. Our results demonstrate the value of high-resolution fault mapping where possible, to discern the maturity, sub-surface linkage and therefore potential earthquake rupture dynamics of active faults.