A significant seismic swarm began in the Campi Flegrei region on October 2, 2025, at 16:38 UTC, indicating a period of increased geological activity.
The Italian National Institute of Geophysics and Volcanology (INGV) recorded at least 20 tremors, with the strongest reaching a magnitude of 2.7 at 19:57 UTC. These shallow events, with hypocenters at a depth of 3 kilometers, are characteristic of bradyseism, a phenomenon involving ground uplift due to subsurface pressure changes. The tremors were felt across the area, notably in Pozzuoli and western Naples neighborhoods.
Residents in Pozzuoli reported hearing a loud boom during a 1.6 magnitude tremor at 16:41 UTC, a common occurrence with shallow seismic events in active volcanic zones. This activity aligns with the ongoing bradyseism in Campi Flegrei, where the ground has been rising at an average rate of approximately 10 millimeters per month since early April 2025.
Previous bradyseismic crises, such as those in 1969-1972 and 1982-1984, also caused significant ground deformation and damage. Historically, Campi Flegrei has experienced intense earthquake swarms preceding eruptions, like the one before the 1538 Monte Nuovo eruption. The 1982-1984 crisis, for example, involved hundreds of felt earthquakes and up to 3 meters of ground uplift, leading to extensive damage in Pozzuoli and the evacuation of 40,000 people.
Recent research, including a study published in Science Advances in May 2025, suggests that these seismic swarms are increasingly driven by pressure buildup in a geothermal reservoir, rather than solely by magma movement. This finding implies that managing groundwater levels could potentially mitigate the risk of such seismic activity. The current swarm, while concerning, is part of a complex geological system that necessitates continuous monitoring and understanding.