From Velocity and Attenuation Tomographies to Rock Physical Modeling: Inferences on fluid-driven earthquake processes at the Irpinia fault system in Southern Italy

We retrieve 3-D attenuation images of the crustal volume embedding the fault system associated with the destructive Ms 6.9, 1980 Irpinia earthquake by tomographic inversion of t* measurements. A high-QP anomaly is found to be correlated with the 1980 fault geometry while the QS model shows regional-scale variations related to the NE edge of the uplifted pre-Tertiary limestone. An up-scaling strategy is used to infer rock properties such as porosity, consolidation, type of fluid mixing and relative saturation percentage at 8-10 km fault depth. We constrain the porosity and consolidation in the ranges 4-5% and 5-9, respectively with the possible fluid mixes being both brine-CO2 or CH4-CO2. The consolidation parameter range indicates high pore pressures at same depths. These results support the evidence for a fracture system, highly saturated in gases and a seismicity triggering mechanism at the fault zone, which is strongly controlled by fluid-induced pore pressure changes.