Fluid-driven slow slip modulates earthquake source migration in the 2010–2014 Mt. Pollino Swarm in Italy

Earthquake swarms driven by fluid migration and aseismic slip are common precursors to larger earthquakes, yet quantitative frameworks to distinguish fluid-induced from tectonic sequences remain elusive. Here we show that the 2010–2014 Mt. Pollino seismic swarm (Southern Apennines, Italy) records the radiative imprint of a long-lived, fluid-pressurized aseismic transient operating in mechanically normal crust. By integrating full moment tensor solutions, Savage–Wood radiation efficiency, pore-pressure diffusion modelling, and global migration-scaling relationships, our results suggest a mechanically partitioned rupture behaviour, whereby events exhibiting positive isotropic components (up to ~ 40%) preferentially occur within the central portion of a high-attenuation fluid-rich domain, whereas high-radiation-efficiency earthquakes preferentially localize along its boundary. The swarm exhibits consistent empirical scaling trends: migration velocity scales as V ∝ T − 0.69 and cumulative moment as M₀ ∝ T⁰·⁷⁶, consistent with the fluid-induced domain of global compilations and implying a reciprocal balance between spatial expansion and energy release. Despite this anomalous kinematics, near self-similar moment-length scaling and stress drops of ~ 1 MPa confirm that fault strength remains typical of tectonic earthquakes. These results provide qualitative scaling indicators for distinguishing fluid-modulated swarms from purely tectonic sequences and highlight the role of aseismic slip and fluid overpressure in shaping seismic hazard in active fault systems.