The area of Phlegraean Fields was marked by a seismic event of strong intensity in the last week, culminating in the earthquake of magnitude 4.4 last May 21st. According to the new weekly bulletin of the INGV Vesuvian Observatory (relating to the period from 18 to 24 May 2026), the seismographs recorded a total of 49 earthquakes14 of which were within an earthquake swarm. Despite the peak of energy released which alarmed the population, the bradyseism remains stable at a lower lifting speed, equal to 10 millimeters per month. Also constant i geochemical parameterswith the temperature of the main fumarole of the Solfatara stopping at 173°C.
Seismicity: 49 shocks and the swarm in the Gulf of Pozzuoli
In the week between 18 and 24 May 2026, the monitoring network located in the Campi Flegrei 49 seismic events. The activity was dominated by the swarm recorded on the morning of May 21 (between 03:50 and 12:00 UTC) in the area of Gulf of Pozzuoli. During this sequence they were detected 14 earthquakesmainly concentrated at a depth between 3 and 4 km.
Within this swarm the most intense shock of the week and of the last period occurred: the earthquake of magnitude Md 4.4which was distinctly felt throughout the Phlegraean area and in Naples.
Ground deformations: Heave remains at 10 mm per month
Data on ground deformations related to bradyseism they show no sudden changes and confirm the trend of recent months. In fact, the Vesuvian Observatory certifies that, starting from the beginning of February 2026, the average lifting speed has stabilized at approximately 10 ± 3 mm monthly. This value represents a clear slowdown phase when compared with the peaks of 25-30 mm/month that had characterized the autumn and winter of 2025.
From the beginning of January 2025 to today, the Rione Terra GNSS station (RITE) has accumulated a total lift of approximately 27.5 centimetres.
On the geochemical front, parameters continue to highlight the known warming trends of the hydrothermal system. The main fumarole (BG) in the Solfatara crater maintained an average temperature value of approximately 173°C. In the Pisciarelli area, however, the average temperature remained around 95°Ca value close to the condensation of the fumarolic fluid.
Summary of the INGV weekly bulletin
Summarizing the data from the latest bulletin (18-24 May 2026), INGV outlines the following situation for the Campi Flegrei:
- Seismology: 49 localized earthquakes, with a maximum peak magnitude of 4.4.
- Seismic swarms: a sequence was recorded on May 21st in the Gulf of Pozzuoli, consisting of 14 close shocks.
- Bradyseism: the rate of ground lifting is confirmed to be stable at around 10 ± 3 mm/month, bringing the total rise from January 2025 to around 27.5 cm.
- Geochemistry and Temperatures: the heating trend of the system continues; the Solfatara BG fumarole confirms averages of around 173 °C.
