Phlegraean Fields: new study identifies a preparatory phase of major seismic events

A new study proposing an innovative reading of seismicity in the Phlegraean Fields has just been published in JGR Solid Earth. By integrating seismic and ground deformation data, researchers from theUniversity of Naples Federico II, the Seismological Research Center of the National Institute of Oceanography and Experimental Geophysics - OGS and the University of Genoa, have identified a clear preparatory phase that precedes major earthquakes, paving the way for future research to develop predictive models capable of estimating their magnitude.

"In recent years, the Phlegraean Fields area has shown a steady increase in seismic activity and ground uplift," says Antonio Giovanni Iaccarino of Federico II University, first author of the paper. "We wanted to understand if these phenomena were connected and if it was possible to recognize common precursor signals before the most significant earthquakes. To do this, we analyzed twenty seismic sequences recorded between 2015 and 2024."

The results of the study, conducted by analyzing in an integrated way seismicity and deformation measurements conducted by the Vesuvius Observatory of the National Institute of Geophysics and Volcanology - INGV, show that before each main event there is a well-defined preparatory phase, during which both ground deformation, i.e. the so-called bradyseism, and seismic energy released by microearthquakes increase. "This correlation," Iaccarino adds, "allowed us to identify a key parameter, residual strain, which describes the balance between deformation and seismicity.

"Scientific studies carried out in recent years by our colleagues, to which our work is added, have shown how crustal deformation at the Phlegraean Fields is the main driver of seismicity," comments Matteo Picozzi, director of the Seismological Research Center (SRC) at OGS. "Understanding this link and defining analytical relationships between the two phenomena is crucial for interpreting the evolution of the system and improving risk assessment."

Using the monitoring data collected by INGV, the research team, also composed of Grazia De Landro (University of Naples Federico II) and Daniele Spallarossa (University of Genoa), has been able to develop a first example of a predictive model for the magnitude of main event seismic sequences. "It is still early to talk about true predictions," Iaccarino continued, pointing out, "Our study represents a first contribution in this line of research. Although the results are promising and the model succeeds, by analyzing the deformation rate and characteristics of small earthquakes, in estimating the potential magnitude of major events several days in advance, the day is unfortunately still far off when similar tools can be used to issue warnings. The uncertainties in the estimates are still large and the risk of false or missed alerts does not make the models usable for civil defense purposes. Our work is a first step in a path of growing knowledge of the generation of strong earthquakes at the Phlegraean Fields that we think will help in the future development of new forecasting tools."

The ability to recognize the preparatory phases of earthquakes represents a new perspective for earthquake and volcanic risk management, not only at the Phlegraean Fields but also in other similar settings around the world. "Many retrospective studies conducted in various parts of the world show us how in some contexts strong earthquakes are anticipated by preparatory phases," Picozzi adds, and concludes, "Understanding how these phases occur and behave by studying the ground deformation and evolution in space and time of small earthquakes," he explains, "can help us make more timely and informed decisions in the event of a crisis.

The research team's goal is to expand the synergistic study between the university, INGV and OGS with new data and apply it to other active volcanic systems."The complexity of the phenomena is well known. I believe that thanks to the joint effort of volcanologists and seismologists and multidisciplinary approaches, we can refine the predictive capacity and take important steps toward increasingly proactive seismic risk management," Iaccarino concludes.

The study was supported by PRIN projects: "Intercepting the PREparatory Phase of lARge earthquakes from seismic information and gEodetic Displacement" (PREPARED - Project Code 2022ZHXWC9); "Relation Between 3D Thermo-Rheological Model And Seismic Hazard For The Risk Mitigation In The Urban Areas Of Southern Italy" (TRHAM - Project Code P2022P37SN); "Multi-Risk sciEnce for resilienT commUnities undeR a changiNg climate" (RETURN), funded by the European Union - NextGenerationEU and the Ministry of University and Research (MUR) under the National Recovery and Resilience Plan (PNRR; Code PE00005).

Original article: Iaccarino, A. G., Picozzi, M., De Landro, G., & Spallarossa, D. (2025). Preparatory phase of major earthquakes during Campi Flegrei unrest (2020-2024). Journal of Geophysical Research: Solid Earth, 130, e2025JB031777 . https://doi.org/10.1029/2025JB031777.