Structure of a normal seismogenic fault zone in carbonates: The Vado di Como Fault, Campo Imperatore, Central Apennines (Italy)

The Vado di Como Fault Zone (VCFZ) is an active extensional fault cutting through carbonates in the Italian Central Apennines. The fault zone was exhumed from similar to 2 km depth and accommodated a normal throw of similar to 2 km since Early-Pleistocene. In the studied area, the master fault of the VCFZ dips N210/54 degrees and juxtaposes Quaternary colluvial deposits in the hangingwall with cataclastic dolostones in the footwall. Detailed mapping of the fault zone rocks within the similar to 300 m thick footwall-block evidenced the presence of five main structural units (Low Strain Damage Zone, High Strain Damage Zone, Breccia Unit, Cataclastic Unit 1 and Cataclastic Unit 2). The Breccia Unit results from the Pleistocene extensional reactivation of a pre-existing Pliocene thrust. The Cataclastic Unit 1 forms a similar to 40 m thick band lining the master fault and recording in-situ shattering due to the propagation of multiple seismic ruptures. Seismic faulting is suggested also by the occurrence of mirror-like slip surfaces, highly localized sheared calcite bearing veins and fluidized cataclasites. The VCFZ architecture compares well with seismological studies of the L'Aquila 2009 seismic sequence (mainshock M-w 6.1), which imaged the reactivation of shallow seated low-angle normal faults (Breccia Unit) cut by major high-angle normal faults (Cataclastic Units). (C) 2016 Elsevier Ltd. All rights reserved.