Seismic Velocity Variations, Ground Deformation and the Role of Fluids During a Low‐Energy Seismic Swarm

On March 9th, 2023, three small earthquakes (38<=Mw<=4.5) occurred near Umbertide (Central Italy), within 4 hours. Analyzing seismic ambient noise in the frequency band 0.1–1 Hz from six seismometers within 20 km of the Mw 4.5, we detect a significant drop in seismic velocity at the time of occurrence of the seismic sequence. A strain sensitivity analysis suggests that crustal damage was primarily caused by the passage of seismic waves, likely enhanced by the presence of fluids. Analyzing geodetic data from recently installed strainmeters and pore pressure transducers, we highlight the role of elastic strain and fluids in driving deformation during this sequence, suggesting the presence of a pressure source that strongly influences the deformation pattern. We find that fluid-induced stress may cause the reloading of a few kPa of a co-seismic asperity within hours, unveiling the contribution of pore pressure sources to the stress budget of seismogenic faults.