An artificial intelligence (AI) model has revealed never-before-seen geological structures at Italy’s Campi Flegrei volcano, including an apparent “ring fault” that could trigger a magnitude 5 earthquake.
So far in 2025, Campi Flegrei has experienced five earthquakes of magnitude 4 or higher, and the volcano has shown signs of instability since 2005. But most of the earthquakes in the region remain undetected, according to a new study that used AI to pinpoint tens of thousands of overlooked seismic events over the past few years.
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Over the past 40,000 years, Campi Flegrei has experienced two of Europe’s largest eruptions, and there is evidence that the volcano’s early history was just as explosive. Scientists have been recording unrest in Campi Flegrei since the 1950s, but monitoring efforts intensified in the 1980s after a swarm of 16,000 earthquakes forced the evacuation of 40,000 residents.
To investigate the modern-day threat posed by Campi Flegrei, Ellsworth and his colleagues developed an AI tool that can identify earthquakes that could not be detected using traditional methods.
Traditionally, seismologists identify earthquakes by analyzing earthquake records. Earthquake records are graphs of undulating lines that represent the shaking of the ground over time. Researchers are looking for sudden increases in small size, a process known as “phase picking,” said study co-author Greg Beroza, a professor of geophysics at Stanford University.
“While this is a simple and often effective means of selecting phases, it does not ‘learn’ how to do it better as it improves over time,” Beroza told Live Science via email. “In our approach, we train a machine learning model to select the phases. We are based on a collection of millions of examples where experts have already done this, and our method is designed to learn how to do this more effectively.”
Beroza said the team decided to analyze Campi Flegrei’s tools before other volcanoes, in part because of the urgent need to better understand the volcano’s behavior. More than 360,000 people live within Campi Flegrei’s 7-mile (11 km) long caldera, and approximately 1.5 million people live in the wider area. The statement said that the unrest over the past two decades has intensified further in 2018, and although there are currently no signs of an eruption, particularly strong or shallow earthquakes could not only damage buildings but also pose great danger to people.
The results of the AI tool, published September 4 in the journal Science, revealed that from 2022 to mid-2025, three-quarters of earthquakes in Campi Flegrei went undetected. Traditional methods would have recorded 12,000 earthquakes during this period, but AI showed that number was closer to 54,000.
By mapping the locations of these earthquakes, researchers discovered faults that had not been revealed by previous methods – cracks in the Earth’s crust that can rub against each other and cause earthquakes. Remarkably, the researchers found that two faults converge beneath Pozzuoli, a town west of Naples that was evacuated in the 1980s. The location of these faults suggests that “earthquakes in the magnitude 5 range are not likely to occur,” Ellsworth said.
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This was not the only surprising discovery. Pozzuoli experienced an uplift in the 1980s, and it’s happening again today, with the ground beneath the town rising about 4 inches (10 centimeters) every year. According to the announcement, it was found that the raised area is surrounded by multiple faults, forming a thin and conspicuous “ring fault” that extends offshore.
“Our Italian colleagues were surprised to see the rings so clearly,” study lead author Xin Tan, a doctoral student in Beroza’s lab, said in a statement. “They expected to see something in the south, where previous data had revealed scattered seismic activity, but they had never seen it so clearly in the north.”
Beroza said seismic activity along the ring fault can help predict changes in the system and could hint at the magnitude of future earthquakes. However, no new information has been obtained regarding the likelihood or timing of Campi Flegrei’s next eruption.
“All of the seismic activity analyzed from 2022 to mid-2025 is shallow, more than 4 kilometers (2.5 miles) deep, and does not indicate magma movement toward the surface,” Beroza said.
The research team’s results on Campi Flegrei indicate that this AI tool could also be useful for other volcanoes. Places with recent increases in seismic activity, such as the Greek island of Santorini, could benefit from a clearer understanding of the underlying geology, the researchers said in a statement.
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