According to a new study conducted by researchers from the National Institute of Geophysics and Volcanology (INGV) and the University College of London (UCL), the presence of two poorly permeable levels in the crust of the Campi Flegrei would regulate the vertical movements and seismicity observed in the last 40 years.
Published in the scientific journal 'Earth and Planetary Science Letters', the research "Evolution in unrest processes at Campi Flegrei caldera as inferred from local seismicity” analyzed the distribution of seismic events and the energy released by them: the results suggest that the latter is mainly concentrated near two levels (separation surfaces between rocks with different physical and chemical properties) located respectively at approximately 3 and at 1-1,5 kilometers depth.
"These levels play a key role in controlling vertical movements and seismicity in the Campi Flegrei and are present in various volcanic systems characterized by high temperatures and fluid circulation. The more superficial one prevents at least in part the dispersion of hydrothermal fluids towards the surface, fluids that have a significant role in triggering seismicity", said Stefano Carlino, researcher at the INGV Vesuvian Observatory and co-author of the study.
Below the deepest level, the rocks change from a brittle behavior, i.e. they are subject to failure, causing earthquakes, to a ductile behavior, in which they deform plastically without breaking.
“Here the process of accumulation of fluids and/or magma takes place which would determine the increase in pressure and the lifting of the caldera. The uplift could continue until the stretching of the crust allows the greater outflow of gas to the surface, with consequent depressurization of the source of the uplift, as we think occurred during the terminal phase of the bradyseismic crisis of 1982-1984, which began with the swarm of 1 April 1984”, says Nicola Alessandro Pino, researcher at the INGV Vesuvian Observatory and co-author of the study.
Unlike the 1982-1984 period, during the current uplift phase underway since 2005, seismicity is concentrated more in the eastern sector of Pozzuoli, below the Solfatara-Bagnoli area.
“This suggests that, in recent years, the ascent of fluids of magmatic origin, with consequent weakening of the rocks, has occurred almost exclusively in this sector of the caldera, where our study has highlighted an increase in the depth of the transition of the characteristics of the rocks from brittle to ductile”, he adds Stefania Danesi, researcher of the Bologna Section of INGV and first author of the study.
As Christopher Kilburn, professor at University College of London (UCL) and co-author of the study, states “The rises of the soil in the Campi Flegrei in recent decades favor the stretching and possible partial rupture of the crust. This process facilitates the passage of fluids accumulated underground and therefore a loss of pressure at depth".
"Monitoring the activity of the Campi Flegrei in the near future may indicate whether or not the seismic swarms of recent months represent the beginning of this phase", concludes Stefania Danesi.
The published research has an essentially scientific value, currently devoid of immediate implications regarding the aspects of civil protection, representing a potentially useful contribution in the future to refine the forecasting and prevention tools of civil protection. At the moment the research results have no direct implication on measures affecting the safety of the population.
Link to the study:
Useful links: National Institute of Geophysics and Volcanology (INGV)
Image from the studio
Conceptual model of the bradyseismic phases of the Campi Flegrei caldera from 1982 to today.
Left: 1982-1984, increase in pressure at depth and lifting of the ground, creation of fractures, depressurization and subsidence; center: 1985-2005, resealing of fractures in the subsidence phase; on the right: 2005-2023, new increase in pressure in depth and lifting of the soil, reopening of fractures, mainly in the crust at the Solfatara