Up to a hundred underground tremors daily: What truly causes earthquakes in Santorini?

The Greek island of Santorini is typically associated with stunning white buildings and blue seas; however, since January 2025, the island has been subjected to an almost continuous series of seismic activities—what is happening? Researchers have sought to answer this question, as reported by IFLScience.

On average, the Seismological Laboratory of the University of Athens records about 90 earthquakes per day with epicenters in the Cyclades region, including Santorini, Amorgos, and Ios. The largest of these earthquakes reached a magnitude of 5. Due to the incredible number of tremors, a state of emergency has been declared on Santorini and Amorgos, leading thousands of locals to leave the island.

It is known that Santorini is no stranger to geological disturbances—the island is volcanic and is still considered active, despite the lack of significant eruptions since the 1950s. While seismic activity could indicate an impending eruption, seismologists believe that volcanic activity is not the source of this current activity.

According to experts from the Seismological Laboratory of the University of Athens, although the seismic activity occurs within the active volcanic arc of the South Aegean Sea, it is not directly linked to any known volcanic center.

Instead, the laboratory experts suggest that the observed activity likely exhibits characteristics of a seismic swarm, as there has been no earthquake with a magnitude significantly exceeding all others that could be classified as a main shock.

A "seismic swarm" refers to a series of relatively small earthquakes often occurring within a short time frame in the same location, without an identifiable "main shock." Researchers now believe that the swarm near Santorini is likely associated with the activation of a system of normal faults—cracks in the Earth's crust where movement occurs. It is thought that the earthquakes result from the sudden release of stress accumulated from movement along these faults.

Seismic swarms, particularly those located in or near volcanic environments, are often triggered by fluid infiltration into the fractured material, which facilitates breaks, combined with stress transfer caused by the tectonic earthquakes themselves. The concerning aspect is that it remains unclear where the volcanic activity will head next. Unfortunately, scientists still lack a precise and effective method to predict earthquakes; however, researchers from the laboratory have proposed several hypotheses regarding potential outcomes.

One of the scenarios predicted by scientists is that the activity will continue with gradually decreasing magnitudes and fewer earthquakes, but will persist over several months.

Another scenario suggests that the swarm may trigger a rupture of a significant portion of a large active fault in the region—this would cause a main earthquake, followed by activity taking the form of a typical aftershock sequence.