In many seismically active countries (e.g., Italy, Greece, Turkey, China, USA) moderate to large earthquakes nucleate in and propagate through heterogeneous (i.e., consisting of carbonate, marly, and clayey deposits) sedimentary successions within the brittle upper crust (< 5 km depth), often causing surface displacement with associated damages and casualities. In particular, in the central Apennines of Italy, moderate earthquakes (< Mw 7.0) propagate through the heterogeneous carbonatic-clayey sedimentary cover up to the Earth’s surface, possibly causing surface faulting (e.g., 1915, Mw 7.0, Avezzano Earthquake; 2009, Mw 6.3, L’Aquila Earthquake. For instance, the mainshock of the recent Mw 6.0 Amatrice earthquake of August 24th, 2016, nucleated at ~7-8 km depth and the seismic slip propagated upward through carbonate rocks causing a ~6 km long surface rupture and deformation. Indirect studies (i.e., through seismological, geophysical, and geodetic techniques) lack of sufficient spatio-temporal resolution to constrain the detailed three-dimensional fault-zone architecture, the deformation mechanisms, and the seismic-related fluid circulation within seismogenic faults at depth. The study of exposed fault zones exhumed from shallow depth (i.e., depths < 3 km) can narrow this knowledge gap and can help in understanding how the shallow fault zone structure can promote or inhibit seismic slip propagation up to the Earth’s surface. For these reasons, in this thesis, I used a multidisciplinary approach to study exposed carbonate/clay-hosted active faults, which can be reliable analogues of buried seismogenic faults at depth, in the seismogenic domain of the central Apennines, Italy. In particular, I combined fieldwork (geological mapping and structural analysis) with laboratory studies. I used optical microscopy and FESEM (Field Emission Scanning Electron Microscopy) to study fault rock microstructures from micro- to nanoscale. I used stable isotope analyses on calcite veins/cement, whole rock geochemistry, cathodoluminescence, and X-ray powder diffraction to study the origin and paleotemperatures of geofluids, which circulated in the fault zones, and fault rock mineralogy. I used low to high velocity friction experiments (using the Slow to High Velocity Apparatus, SHIVA, at INGV in Rome) to understand fault rock frictional properties during earthquake propagation and in situ mechanical analyses using Atomic Force Microscopy to understand fault rocks elastic properties (Young’s modulus and viscoelasticity) down to nanoscale. In particular, the main focus of this thesis is to understand the roles both of fluids and phyllosilicates during the seismic cycle within carbonate-hosted faults in the shallow carbonate-dominated brittle crust
