A magnitude 4.6 earthquake on June 30, 2025, centered in Bacoli, jolted the Campi Flegrei region near Naples, causing considerable disruption to the local rail infrastructure.
The seismic event, occurring at a shallow depth of approximately 4 kilometers, was felt across multiple districts of Naples. In response to the tremors, authorities immediately halted services on the vital Cumana and Circumflegrea rail lines, which are crucial for connectivity in western metropolitan Naples. To maintain commuter mobility, replacement bus services were put into operation.
This seismic activity is part of a broader pattern of escalating unrest in the Campi Flegrei, a vast volcanic area situated northwest of Naples. The region has been experiencing notable ground uplift and an increase in seismic events since 2018, leading to continuous monitoring by scientific and governmental agencies.
Recent scientific analysis, published in May 2025, suggests that the persistent ground deformation and earthquake swarms in the Campi Flegrei caldera are primarily driven by rising pressure within a geothermal reservoir, rather than magma or gases. This research indicates that managing groundwater levels could potentially mitigate these risks. The study, which involved subsurface imaging and laboratory experiments, demonstrated how the 'self-healing properties' of the caprock can create a closed system that leads to deformation and seismicity. This finding offers a new perspective on the underlying mechanisms of the region's unrest, suggesting that interventions related to water management could play a role in reducing seismic hazards.
Historically, Campi Flegrei has a significant volcanic past, with major eruptions occurring approximately 40,000 and 15,000 years ago. The last eruption in 1538 created the Monte Nuovo hill. The current period of unrest, characterized by ground uplift and increased seismic activity, has been ongoing since 2005, with a notable acceleration in recent years. The Italian National Institute of Geophysics and Volcanology (INGV) has been diligently monitoring the area, with efforts focused on modernizing its multi-parametric monitoring networks to ensure comprehensive coverage and a deeper understanding of ground shaking. This ongoing vigilance is essential for providing effective support to civil protection actions and safeguarding the rich cultural heritage of the Neapolitan area.