M4.4 earthquake triggers seismic swarm at Italy’s Campi Flegrei caldera
A shallow M4.4 earthquake struck the Campi Flegrei caldera west of Naples, Italy, at 05:50 LT (03:50 UTC) on May 21, 2026, beginning a seismic swarm that ended after 12 earthquakes.
Earthquake swarm Campi Flegrei, Italy on May 21, 2026. Credit: TW/SAM, ESRI
A shallow M4.4 earthquake struck the Campi Flegrei caldera west of Naples at 03:50 UTC on May 21, 2026, beginning a seismic swarm in the Gulf of Pozzuoli.
The Italian National Institute of Geophysics and Volcanology (INGV) said the earthquake had a depth of about 3 km (1.9 miles) and was the strongest event in today’s sequence. The swarm consisted of 12 earthquakes before it was announced finished at 12:01 UTC. The events were concentrated offshore between the Pozzuoli and Bacoli sectors of the caldera.
The main shock was felt across the Naples area, prompting local checks and precautionary closures. Officials at the Municipality of Naples ordered precautionary school closures in the Bagnoli-Fuorigrotta “Red Zone” while inspections are carried out on public and private buildings.
The sequence occurred during the continuing bradyseismic unrest at Campi Flegrei. INGV previously stated that about 23 000 earthquakes were recorded during the current bradyseismic crisis through 2024.
Campi Flegrei (Phlegraean Fields) is a large volcanic caldera west of Naples, spanning about 12 km (7.5 miles) across and partly extending beneath the Gulf of Pozzuoli. The volcanic field contains more than 20 craters and volcanic edifices, including the Solfatara crater, and sits within one of Europe’s most densely populated volcanic regions.
The caldera formed through two major explosive eruptions, including the Campanian Ignimbrite eruption about 39 000 years ago and the Neapolitan Yellow Tuff eruption about 15 000 years ago, while its most recent eruption formed Monte Nuovo in 1538.
About 3 million people live in the wider Naples metropolitan area, while several hundred thousand residents live within or immediately adjacent to the Campi Flegrei caldera, making the area one of the world’s highest volcanic-risk urban environments.
References:
1 Terremoto di magnitudo Md 4.4 del 21-05-2026 ore 05:50:52 (Italia) in zona: Campi Flegrei – INGV – May 21, 2026
2 Evento sismico, Md 4.4, ai Campi Flegrei e comunicato di sciame: 21 maggio 2026 – INGV – May 21, 2026
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Super prominent VLPs preceding the M4.
Our timings suggest about 2.5-3km. INGV errs deeper, comfortably take 10% off their figures. We have tighter X,Y,Z figures than INGV. Using their own data, lol.
Puts it in the stretched zone where dyke-like structures are ducting the gases and fluids. Prediction that the rebound will be increased uplift on the eastern flank.
Pile of rubble.