Clusters of earthquakes have been shaking southern Italy with growing strength since 2022, posing risks to hundreds of thousands of residents who live above an active zone called Campi Flegrei, characterized by gradual uplifts and sinkings of the terrain.
As officials deliberate over strategies for responding to disasters and establishing evacuation procedures, scientists might have uncovered a method to prevent this cyclical instability entirely: through controlling water runoffs or decreasing groundwater levels, which would consequently lessen the fluid pressure inside the geothermal reservoir.
Using subsurface imaging techniques and laboratory experiments, researchers at Stanford University demonstrated that the accumulation of pressure from water and steam within the reservoir beneath Campi Flegrei could trigger earthquakes once the caprock, also known as the seal, becomes impermeable.
The research, published in
Science Advances
Indicates that the reappearance of an over-pressured reservoir caused deformations and seismic activity both in the early 1980s and during the last fifteen years, which eventually helped in pinpointing the root cause.
These discoveries contradict the prevalent hypothesis suggesting that tremors result from magma or its gas ascending due to melts moving upwards from deeper zones toward more shallow regions beneath volcanoes. Additionally, they highlight how the pace at which water slowly replenishes the storage chamber affects both the speed of ground deformation and variations in terrain elevation.
“To tackle this issue, we have options such as controlling surface runoff and water movement, or possibly alleviating stress by extracting liquids from wells,” explained Tiziana Vanorio, the lead researcher for the study and an associate professor of Earth and planetary sciences at the Stanford Doerr School of Sustainability.
The researchers examined repeated trends and shared features in the images of underground formations and seismic activity during Campi Flegrei’s two latest episodes of instability.
Characterized by land uplift and burst-like shaking, accompanied by rumbling sounds that have become a signature feature for the population, scientists suspect this activity signals steam-driven explosions, triggered when liquid water rapidly flashes to steam during fracturing caused by earthquakes. The study includes data from the unrest of 1982–1984 and 2011–2024.
“We have been looking at something that occurred decades apart, but there are profound similarities in the imaging, which point not only to a cyclical pattern of the phenomenon but also to a common underlying cause,” said co-author Grazia De Landro, a researcher at the University of Naples Federico II, Italy, and visiting scholar at Stanford.
The concept of collaborating began from this point, particularly when considering rock physics. Employing rock physics is essential for making quantifiable statements regarding the imaging beneath the Earth’s surface.
The Campi Flegrei volcanic region contains an enclosed geothermal reservoir located underneath the city of Pozzuoli, which lies west of Naples and near Mount Vesuvius. Continuous monitoring began after the period of increased activity between 1982 and 1984, during which time the ground ascended over six feet, causing Pozzuoli’s port to become too shallow for vessels to reach shore. Following this event, a significant magnitude-four quake along with numerous smaller tremors led to the relocation of approximately 40,000 residents from Pozzuoli.
“The past three years have presented significant challenges. Numerous structures have suffered damage due to persistent tremors, leaving many without places to live,” stated Vanorio, who spent his childhood in Pozzuoli and had to relocate in the 1980s.
As a citizen today, this project represents my objective more so than merely being a geophysicist, since the research indicates that we can manage unrest instead of solely monitoring it, thus paving the path for prevention.
Land that ‘breathes’
Campi Flegrei is an 8-mile-wide caldera, a large basin created by significant volcanic events around 39,000 and 15,000 years ago, leading to the sinking of the ground’s surface.
The caldera experiences uplift and subsidence, with the land rising and sinking, even without an eruption. After the unrest in 1982–1984, the area sank by about 3 feet. For subsidence to occur, mass must be released from the subsurface, which can include magma, water, vapor, and carbon dioxide.
People living in Pozzuoli observe the caldera’s movements, which involve releasing gases and causing the land to shift, often rising or falling by several meters within a brief period.
Traditionally, an increase in elevation in volcanic regions has been broadly attributed to magma-related replenishment activities. This assumption posits that magma and/or its gases play key roles in causing deformations followed by seismic events. However, the research suggests this might not universally hold true.
Although certain scholars started investigating the connection between precipitation and seismic activity over the past ten years, the research elucidates that it isn’t the rain per se, but instead the pressure caused by the gradual buildup of water in a confined reservoir that triggers fracturing—and as a result, causes tremors—according to Vanorio.
Vanorio noted that we have observed an increase in yearly fluctuations in precipitation over the past 24 years. Therefore, it’s crucial to track the buildup of underground water reserves or to ensure proper management of surface water flow.
A closed system
A distinctive characteristic of Campi Flegrei is the
fibrous nature
Atop the caprock above the geothermal reservoir, fibrous materials find application in engineering due to their ability to stretch significantly before breaking. These materials have the capacity to store strain over time. In a volcanic setting, this accumulated stress might ultimately result in an abrupt explosion of scalding water, steam, and volcanic debris.
Over a span of 24 years, the researchers studied rainfall patterns, the direction of underground water movement, and the mechanism of caprock sealing to comprehend the refilling of the geothermal reservoir and the resulting increase in pressure. At Vanorio’s Rock Physics and Geomaterials Laboratory, they showed that fissures within the caprock seal due to chemical reactions between the rock’s minerals and hydrothermal water and steam.
To examine the properties of the caprock, the researchers performed tests utilizing a hydrothermal vessel similar to an appliance well-known to many Italians: a moka pot, or stovetop coffee maker.
They packed the lower section with brine and the upper part with volcanic ash and pulverized rocks characteristic of Campi Flegrei, before heating the container to the temperature observed in the geothermal reservoir. By the next day, mineral fibers had developed, and fissures within the rocky layer quickly closed via cementation.
This creates a closed system that allows fluid pressure to build up until it fractures the surrounding rock. Fracturing from earthquakes causes a sudden drop in fluid pressure as liquid water flashes into steam and escapes. “That produces explosive bursts and booming sounds typical of the area,” Vanorio said.
The researchers applied multiple disciplines to reveal how Campi Flegrei operates as a closed system, including tomography of the subsurface, which De Landro carried out using earthquake records to construct images of the subsurface that can be analyzed like a CT scan.
“Using geophysical techniques to image the subsurface is akin to an antique doorbell; it lets us know that someone is at the entrance, but not who exactly it is. Therefore, interpreting tomography images requires validation in the lab—this is what lends such strength to the partnership between seismology and rock physics,” explained Vanorio.
A new model
The analyses of the tomography alongside the locations and extents of earthquakes helped researchers formulate their hypothesis that repeated tremors might not be caused by magma refilling or gas emissions within the system. In both instances of instability, the initial seismic activity started beneath the caprock at an approximate depth of one mile.
After observing the temporal progression of earthquakes, a distinct trend becomes evident—the earthquakes become deeper as time progresses,” explained co-author Tianyang Guo, a postdoc researcher in Earth and planetary sciences, who merged seismic information from both events for interpretive analysis.
If magma or its gases moving upward was indeed the main cause of the increased activity, we’d anticipate seeing earthquakes originating from deeper regions near where the molten rock resides—at around five miles beneath the Earth’s crust—and then gradually shifting towards more shallow areas as suggested by experts. Additionally, Vanorio pointed out that the sinking ground observed after this period of heightened volcanic behavior can’t be accounted for solely by magma ascending without causing an eruption.
One possible explanation for subsidence could be the recorded release of water and vapor following hydraulic fracturing due to seismic activity, which inherently reduces pressure inside the reservoir.
Using their updated model of Campi Flegrei’s internal processes, the scientists aim to explain the mechanisms triggering instability within this volatile system to the relevant authorities in the local Italian administration.
Vanorio refers to this as a perfect geological storm—where you have all the elements for such an event: the heat source within the system, represented by the molten magma; the energy stored in the geothermal reservoir acting like fuel; and the cap that seals everything in place.
We cannot control the burner directly, yet we possess the capability to oversee the fuel. Through the restoration of waterways, surveillance of underground water levels, and regulation of reservoir pressures, we can transition earth sciences towards a more preemptive strategy akin to preventative medicine. This method allows for early risk detection and prevents instability from escalating. In this way, science supports societal well-being.
Davide Geremia, a former postdoctoral scholar in Vanorio’s lab, is a co-author of the study.
More information:
Tiziana Vanorio, The Recurrence of Geophysical Manifestations at the Campi Flegrei Caldera,
Science Advances
(2025).
DOI: 10.1126/sciadv.adt2067
.
www.science.org/doi/10.1126/sciadv.adt2067
Provided by Stanford University
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