Scientists Link 25,000 Santorini Quakes to Wave-Like Magma Intrusion

Earlier this year the Santorini region was shaken by an extraordinary earthquake swarm: roughly 25,000 tremors across a little more than a month. New research using precise earthquake locations, machine-learning relocation tools and novel stress-analysis methods reveals what likely triggered the unrest.

Studies published in Nature and Science show a consistent picture: magma began creeping into a chamber beneath Santorini in mid-2024, and starting on 27 January 2025 a sustained swarm of earthquakes followed. The accumulated events—some approaching magnitude 5.0—prompted local authorities to declare a state of emergency before activity subsided in early March, with only one isolated quake recorded in late May.

The new analysis by a team at University College London reconstructs how the magma moved. About 10 kilometers below sea level, vertically oriented sheets of magma intruded and propagated horizontally through a rock package roughly 20 kilometers thick. The authors liken the intrusions to a knife scraping across a loaf of bread: each sheet passed along the rock, producing repeated, wave-like stress changes that registered at the surface as thousands of earthquakes.

"We used a new method to work out the cause of a swarm of earthquakes, treating each of the 25,000 precisely located quakes as 'virtual stress meters'—clues as to how stress was changing underground," said Stephen Hicks, co-author from University College London. "This gave us a robust and higher-resolution picture of what was happening, allowing us to rule out fault slippage as the earthquakes' main cause."

The team found the magma entered an underground reservoir that links the Santorini caldera with the nearby Kolumbo submarine volcano, but the intrusion lacked the pressure and buoyancy needed to drive an eruption. Co-author Eleftheria Papadimitriou of Aristotle University of Thessaloniki notes that this rebounding, wave-like intrusion "may not be unique to Santorini but may be a fundamental mechanism by which magma is transported beneath volcanoes worldwide."

These findings refine how scientists interpret volcanic seismic swarms and could improve hazard assessment by distinguishing magmatic intrusion from tectonic fault slip. While Santorini's explosive past—most famously the massive Thera eruption around 1600 B.C.E.—remains a part of the island's history, current research suggests the recent unrest was a deep magmatic process that did not culminate in an eruption.

Sources: Research published in Science and Nature; quotes from study co-authors Stephen Hicks (UCL) and Eleftheria Papadimitriou (Aristotle University of Thessaloniki).