Interdisciplinary Risk and Crisis Management Committee of NKUA Issues Statement on Seismic Activity in Santorini - Amorgos

Between February 2 and the early hours of February 5, 2025, seismic activity in the Santorini-Amorgos region has intensified further. Seismological data analysis up to February 3, updated using machine learning, recorded over 1,300 earthquakes on February 2 and more than 1,400 on February 3. The total number of earthquakes from January 26 to February 3 has exceeded 6,400, with over 4,800 having a magnitude of M≥1.0 and more than 800 measuring M≥2.5.

The number of M≥2.5 earthquakes has been steadily increasing daily, with recorded counts of 0, 1, 2, 6, 9, 25, 45, 340, and 437 earthquakes from January 26 to February 3. On February 2, five earthquakes with M≥4.5 were recorded, followed by seven on February 3 and nine on February 4. The strongest recorded earthquake so far was M4.6 on February 2, while February 3 and 4 saw three quakes between M4.9-5.0 and four more with M4.8. As of early February 5, seismic activity remains concentrated near Anydro, with over 30 new earthquakes recorded, the largest reaching M4.4.

Seismic Migration and Potential Risks

On February 2, earthquake epicenters were initially concentrated midway between Anydro and Santorini, later migrating northeast towards Anydro. On February 3, seismicity remained clustered southwest of Anydro, with smaller clusters forming west and north of the island, generally within 10 km.

By February 4, seismic activity had expanded west of Anydro and slightly eastward. Between February 1 and 4, the most active seismic zone shifted northeast at a speed of ~4-5 km/day, following a N40°E direction. Machine learning analysis suggests that, during certain seismic surges, migration rates increased, covering smaller distances at a faster pace.

Is This a Seismic Swarm or a Precursor to a Major Earthquake?

Current seismic activity in the Santorini-Amorgos region resembles a seismic swarm, as no single earthquake is significantly stronger than the rest, ruling out a clear mainshock. Additionally, seismicity continues to rise, with aftershock sequences following a decreasing pattern in frequency and magnitude, typically with aftershocks being ~0.5 magnitude units smaller than the largest preceding quake.

There are two possible scenarios:

Seismic Swarm Continuation: If the activity follows the pattern of the Thebes seismic swarm, it may persist for months with gradually decreasing magnitude and frequency.
Major Earthquake Triggered: The swarm could stress a major active fault, leading to a stronger main earthquake followed by a typical aftershock sequence. In hindsight, this would then be considered a foreshock sequence.

Although this seismic surge is occurring within the South Aegean Volcanic Arc, it is not directly linked to a volcanic eruption. Instead, it appears to have activated a normal fault system (SW-NE direction) in the Anydro basin. Seismic swarms in volcanic regions often result from fluid intrusions into fractured rock formations, combined with stress redistribution caused by tectonic quakes.

Monitoring Efforts Intensify

Seismic detection capabilities are expected to improve in the coming days as all agencies within the Unified National Seismograph Network work to densify local monitoring stations.

To enhance real-time monitoring, experts from the Seismology and Geophysics Laboratories at NKUA and the Interdisciplinary Risk and Crisis Management Committee will deploy to Ios and Santorini for the installation and maintenance of seismographs and to conduct ground deformation measurements.

This developing situation will require close monitoring to determine whether the ongoing seismic swarm remains within expected patterns or escalates into a larger event.