Positive Isotropic Components From Full Moment Tensor Inversion and Fluid Involvement in the Pollino (Italy) Seismic Swarm

ABSTRACT We computed full moment tensor inversion for 65 seismic events (2.6 ≤ M ≤ 5.2) of the 2010–2014 Mt. Pollino (Italy) seismic swarm. A probabilistic inversion approach was applied to estimate moment tensor and its uncertainties, and the stability of the solutions was tested using three velocity models. Stable and reliable solutions were obtained for 49 earthquakes. The sources are characterised by a dominant double‐couple component (50%–90%) and significant positive isotropic contribution (25% on average). The isotropic component indicates co‐seismic volumetric changes, consistent with tensile faulting promoted by over‐pressurised fluids within a highly fractured crust. Our results, together with previous seismological studies, suggest that the Pollino swarm developed in a highly fractured seismogenetic volume where high fluid pressure weakened the fault zones and facilitated rupture. The exact nature and composition of these fluids remain uncertain and should be addressed by future multidisciplinary investigations.