An innovative “seismic tomography” technique has allowed, for the first time, to observe the internal structure of the Campi Flegrei Caldera. The result is the result of the work of researchers from the National Institute of Geophysics and Volcanology (Ingv) and the University of Milan Bicocca, and as described in the study published in the journal Earth and Planetary Science Letters, it allowed us to reconstruct the movements of the magna until to a depth of six kilometers, and could therefore prove invaluable in the future for monitoring seismic and volcanic activity in the area.
The new approach is an evolution of the more traditional seismic tomography, i.e. the study of the morphology of the subsoil based on the analysis of the propagation time of seismic waves. With traditional techniques, in fact, it is difficult to obtain a satisfactory resolution below a certain depth. While the one described in the new study, which the researchers define as a “nonlinear probabilistic approach”, made it possible to precisely study the changes that occurred within the caldera between 1984 and 2022, up to a depth of six meters.
Precisely this ability to study the evolution over time of the magmatic accumulation zones is one of the main new elements, the result of an intuition that has allowed the development of what the researchers define as 4D seismic tomography, understood as mapping of the three dimensions of space plus the fourth, which is precisely time.
Comparison with the past
The study thus made it possible to compare what happened in the previous bradyseismic crisis (i.e. periods in which the ground in the Campi Flegrei caldera begins to rise, causing earthquakes), that of 1982-1984, and the current one, which began in 2005. And the results demonstrate that the two cycles, although involving different volumes, were both characterized by episodes of ascent and accumulation of magmatic gases under overpressure in the central area (the reservoirs positioned at 2.5 and 3.5 kilometers deep), and of magna at depth (in the reservoir previously unreachable by analysis, located at 5 kilometers depth), suggesting that both these processes play an important role in inducing caldera unrest.
The approach may therefore prove useful for monitoring the evolution of the Campi Flegrei volcanic system over time, and therefore could help to somehow predict the risks for the population, and for this reason the researchers are already working to extend their model also to the years following 2022.
The current situation
Meanwhile, the situation in the caldera area is under close monitoring, after last September's earthquake which, with a magnitude of 4.2, was the most powerful in the last 40 years. Mauro De Vito, director of the INGV Vesuvian Observatory, recalled on the occasion of a meeting with the citizens of the western area of Naples that the raising of the soil in the Campi Flegrei has proceeded in the last month at a rate of 20 millimetres, the double compared to January this year.
“This means that the phenomenon, but you can also see it from the number of earthquakes and the magnitude, is increasing,” explained De Vito, interviewed before the meeting. “It is also possible that slightly larger earthquakes of slightly greater magnitude could occur. But we are always talking about medium magnitudes, not high ones. The average magnitudes are quite typical of this area, very similar to those observed in the years 1982-1984 relating to the previous bradyseismic crisis”.