The seismic crisis that gripped the Greek island of Santorini and its neighbors last year contained more than 60,000 earthquakes, according to a unique machine learning study that identified the earthquakes as they occurred between December 2024 and June 2025.
At the 2026 SSA Annual Meeting , Stanford University Ph.D. student Xing Tan described how he and his colleagues monitored the remarkable sequence as it unfolded, using the resulting high-resolution earthquake catalog to define a network of faults in the region and to follow the rapid migration of seismicity.
The research team identified 46 recurring seismicity bursts of hundreds of earthquakes occurring within one to two hours. During some of these bursts, seismic migration sped along the fault zones at speeds of up to 2 kilometers per hour.
The speed and pattern of the seismicity observed by Tan and colleagues lends further support to the idea that the earthquake sequence was caused by intrusion of magma related to the region’s volcanoes.
Most researchers use machine learning techniques to pore through seismic data months after its collection. The study by Tan and colleagues is unusual in that it used these techniques to follow the event as it evolved.
“What’s particular about this sequence is that it’s really intense. There can be hundreds of earthquakes in an hour,” Tan said. “For machine learning, we can build a lot of algorithms, and we can run them in parallel to process a huge amount of waveforms, mostly even in real time. So we can pick thousands and thousands of earthquakes during this crisis.”
These methods have only been used in limited ways in real-time operations, said Stanford seismologist and study co-author Gregory Beroza.
“For something like this, a volcanic crisis that is maybe rapidly unfolding, I think we have to transition from the status quo where these methods aren’t used,” said Beroza, who also directs the Southern California Earthquake Center. “It should be operational, that is, at least part of a routine approach for providing better information during an event.”
The approach identified six times more earthquakes for the first 30 days of the sequence compared to the number identified by traditional regional seismic monitoring, Tan said, while providing the information the researchers needed to pinpoint the location of these events.
“We were trying to focus on really short periods of time, for example, one hour,” he said. “We want to see all the earthquakes going in one hour, how they are distributed, how the seismicity looks as it migrates. With such a rich data set, we can learn more about what’s happening during these very short periods of time.”
The researchers uncovered a network of northeast-southwest-trending faults extending from northeast of Santorini to the southwest of the island Amorgos, passing beneath Anydros Island. The seismic sequence began at the southwestern end of the system and propagated northeastward.
The pattern of bursts resembles those seen at other volcanoes where magma forms intrusive dikes at speeds of a few kilometers per hour. However, this type of activity is usually found in volcanoes like those in Hawai’I and Iceland where the magma is rich in magnesium and iron and flows freely.
The volcano system in the Greek islands typically produces cooler, more silica-rich magma, which is more viscous and explosive.
The earthquake data could suggest that “there actually is low viscosity magma at great depth under Santorini, which could explain why it can move so fast,” Beroza noted, suggesting that the magma may be modified to become more viscous as it interacts with the crust.
In another talk at the SSA meeting, a research team led by Marius Isken of GFZ Postdam shared the results of their study that suggests the Santorini and Kolumbo volcanoes might share a deep magma plumbing system .
“Historically, this area has had very large eruptions, including the one that destroyed the Minoan civilization about 3600 years ago, so it’s something to keep watching,” Beroza said.
And in 1956, a magnitude 7.7 earthquake sequence in Amorgos and Santorini led to a major tsunami in the Aegean Sea, Tan noted. “It’s a very complicated area, both volcanically and tectonically.”