In the area of Campi Flegrei The presence of seismic swarms was detected “burst-like”, Seismic sequences ad very high frequencyrecorded by the seismograms in the area of the Solfatara between the 2021 and the 2024. The discovery is reported by a new studyconducted by researchers of theIngv and of the CNR and published on Nature Communications. These shamans would be the result of the growing Increase in pressure exercised fluids infiltrated in the rocce fractures in the subsoil and can be considered as an indicator of growing instability in the hydrothermal system. The Campi Flegrei area is going through a prolonged period of Intensification of volcano-tetty activitystarted in 2005. In this period of time, an increase in the seismicity general, an intensification of theemission of gas e an acceleration of the soil deformation.
Seismicity and Bradisism in the Flegrei fields and the study on Burst-Like shamans
The last bradisismic phase of the Campi Flegrei began in 2005 and saw the succession of beyond 18,500 earthquakeswith a maximum magnitude of 4.4 degrees Richter and soil lifting peaks up to 1.4 meters in the central area of the Caldera. In particular, the area including the hydrothermal system Solfatara -PisciarelliThe Monte Olibano and also the Gulf of Pozzuoli is among the most affected by bradyseismic activity, with beyond 10,000 Registered seismic events. The earthquakes of the Flegrei fields are usually of the volcano-tettonic type, that is, they have a clear and generally impulsive start, a large frequency content and are associated with fragile fracture mechanisms of the rocks, similar to those of the tectonic earthquakes. Between 2021 and 2024 it was observed an intensification of the activity of the volcano-tettoonics in the areaboth in terms of frequency of seismic and soil lifting rate.
A study conducted by researchers of theNational Institute of Geophysics and Volcanology (Ingv) – Vesuvian Observatory and Section of Pisa – together withInstitute for the electromagnetic detection of the environment of CNR of Naples, and published the11 February 2025 In the international magazine Nature Communicationshighlighted how some seismic sequences recorded in this period can be traced back to shamans burst-like, or more simply, Shades with burst.
The hypocenter of these seismic sequences are generally a few km deep and show a more evident distribution below the crater of the Solfatarawith a slight shift towards northin correspondence of the hydrothermal system of Solfatara -Pisciarelli.
What are “burst” seismic swarms
Burst type seismic swarms are characterized by intermethlythat is, the average time between one event and the other, extremely reduced that can be lower than a few seconds. The seismogram appears chaoticwith events that follow one another irregularly and with largely overlapping seismic peaks, to the point of make individual earthquakes difficult to distinguish and the related inter -interpretations.
These phenomena were described for the first time in 1990 in the hydrothermal area of Mammoth Mountainsin United Statesand were interpreted as the result of rapid pressure variations within the local geothermal systemcaused by the gas movement in the subsoil of the volcanic complex. Burst -type seismic swarms were then identified in other volcanic contexts: in 1992 a White Island (New Zealand) and in the volcanic area of Tatuna Taiwan. In both cases, these sequences were interpreted as the response of the fault system and fractures in the subsoil to fluid pressure fluctuations. In the 2005in JapanBurst-Like Shames were associated withFreetic eruption of the volcano Hakone.
The source of the burst type swarms of the Campi Flegrei
As in the cases mentioned above, also for the Flegrei fields the authors of the study suggest that the “burst” seismic swarms can reflect the fragile response of the rocks of the subsoil to the increases in pressure of fluids in the hydrothermal system. In fact, several studies have highlighted how, in recent years, the Flegrei field area has been affected by a progressive increase in pressure and temperature in the subsoil, phenomena attributable to the ascent of deep gases and magma.
In particular, the Solfatara -Pisciarelli area is characterized by a regime of Extension stress. It is, in fact, ageodetic anomalythat is, an area of the caldera in which the lifting of the soil takes place at generally lower speeds compared to the surrounding areas. This relaxation in the most superficial crustal layers is attributed to the inflation of the caldera, that is, the lifting of the soil caused by a deformation source located in depth.
The tectonic essential efforts would encourage a increase in the permeability of the rocks, As a result of the fracturein the deepest hydrothermal system, creating ideal conditions for the circulation of fluids and gas. This process would be the basis of the burst type seismic swarms, generated by the push of the same fluids against the fracture surfaces, but could also prepare the area to the development of Future Freatics activity.
Sources
