Earthquake swarm at Campi Flegrei, Italy

campi flegrei ingv 7 days to may 18 2024 earthquakes

A new earthquake swarm began in the Campi Flegrei area, Italy at 04:06 UTC on May 18, 2024.

  • Today’s swarm follows a series of more than 1 100 earthquakes over several months in 2023, including M4.2 — the strongest quake in the area in 40 years.
  • These events sparked public concern and prompted officials to discuss new safety measures for more than 500 000 residents living in the towns and villages surrounding the volcano.

Between 04:06 and 05:30 UTC on May 18, INGV registered 16 earthquakes in the area with magnitudes up to Md2.8 ± 0.3.

The M2.8 earthquake at 04:30 UTC was initially recorded as M3.7. This discrepancy occurred because numerous small seismic events overlapped, distorting the initial reading, INGV said.

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Location of today’s M2.8 earthquake in Campi Flegrei, Italy. Image credit: INGV

The quakes are occurring at depths between 2.3 and 2.8 km (1.4 – 1.7 miles).

“Updates will follow as the phenomenon evolves,” the agency said.

In October 2023, the Italian cabinet discussed a series of new measures designed to ensure the safety of the more than 500 000 residents in towns and villages surrounding Campi Flegrei. The measures included building assessments, following months of seismic activity that has featured over 1 100 earthquakes, with the strongest registering a magnitude of 4.2. This was the most powerful earthquake in the region in the last 40 years.

Experts attributed the heightened seismic activity to a geological phenomenon known as bradyseism. This is characterized by a cyclical rise or fall in the Earth’s surface due to the filling or emptying of underground magma chambers. Currently, the ground around Campi Flegrei is rising by 1.5 cm (0.6 inches) per month, sparking concerns about the structural integrity of local buildings.

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Campi Flegrei is a 13 km (8 miles) wide caldera that encompasses part of Naples and extends to the south beneath the Gulf of Pozzuoli.

It is the largest active urbanized caldera in the heart of the European continent and is classified as a supervolcano due to its potential for producing extremely large and explosive eruptions, as evidenced by past events like the Campanian Ignimbrite and Neapolitan Yellow Tuff eruptions.

Episodes of significant uplift and subsidence within the dominantly trachytic caldera have occurred since Roman times. The earliest known eruptive products are dated 47 000 years BP. The caldera formed following two large explosive eruptions, the massive Campanian ignimbrite about 36 000 BP, and the over 40 km3 (10 mi3) Neapolitan Yellow Tuff (NYT) about 15 000 BP.

Following the eruption of the NYT a large number of eruptions originated from widely scattered subaerial and submarine vents. Most activity occurred during three intervals: 15 000 – 9 500, 8 600 – 8 200, and 4 800-3 800 BP.

The latest eruption was in 1158 CE at Solfatara and activity in 1538 CE formed the Monte Nuovo cinder cone.

campi flegrei italy
Image credit: INVG

Since 2005, Campi Flegrei has been affected by the bradyseismic phenomenon which causes ground lifting, earthquakes and fumarolic emissions.

“The caldera is monitored by a continuous multi-parameter monitoring system. All the data provided by this system, at the moment, do not show evidence of the imminence of a volcanic eruption, much less of large proportions,” INGV volcanologists said on April 17 and cautioned the public that statements made in some media about the catastrophic effects of the future eruption at Campi Flegrei were not true.

Since 2012, hazard studies have been employed to define the most probable eruptive scenarios in the area. The scenario with the highest probability is a small eruption, similar to the Monte Nuovo eruption of 1538.

However, for evaluating areas potentially exposed to various phenomena during a future eruption, the reference scenario is based on the most intense phase of a medium-scale eruption, like the one that occurred at Astroni 4 000 years ago. This scenario forms the basis for emergency planning, identifying areas exposed to different types of hazards, such as pyroclastic flows for the red zone and ash fall for the yellow zone.

A significant characteristic of the Phlegraean caldera, and calderas in general, is the difficulty in predicting the location of an eruptive vent. This uncertainty complicates the identification of areas potentially exposed to hazardous phenomena. To address this, areas impacted by pyroclastic flows and ash fall were determined by considering all possible positions of a new eruptive vent.

The likelihood of the next eruption being similar to the Campanian Ignimbrite or Neapolitan Yellow Tuff events is very low.

These large-scale eruptions require an enormous influx of magma into the system, which would generate significant signals detectable by the monitoring system and the local population. For context, prior to the last period of activity—during which 27 explosive eruptions occurred with a total magma volume of less than 3 km3 (0.7 mi3) —the area between Monte Nuovo and Pietra rose by approximately 50 m (164 feet).

“During the two most devastating eruptions (Campanian Ignimbrite and Neapolitan Yellow Tuff), tens to hundreds of cubic kilometers of magma were erupted in a single event. Such phenomena could not occur without notable and detectable precursors,” the agency said.

Updates

10:17 UTC, May 21

A new seismic swarm started at Campi Flegrei area, Italy at 17:51 UTC on May 20, 2024. Local Earthquake monitoring network has detected around 150 quakes within the next couple of hours, with the strongest being M4.4 — now the strongest quake to hit the caldera region since the beginning of the current bradyseismic crisis in 2005. Preventive evacuations have thus far affected 36 families.

References:

1 CAMPI FLEGREI | Precisazioni su Magnitudo durata (Md) dell’evento sismico del 18 maggio 2024 delle ore 06:30:55 (ora locale) – INGV – May 18, 2024

2 CAMPI FLEGREI | L’INGV chiarisce rischio eruttivo e pericolosità – INGV – April 17, 2024

3 Campi Flegrei – Geological summary – GVP

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