Since 27 January 2025, the region around Santorini, known as the Cyclades, has experienced an intense surge in seismic activity, with over 1,000 undersea earthquakes recorded, which have been characterized as a ‘seismic swarm’ or ‘earthquake swarm’.
Several tremors have exceeded magnitude 5.0, with epicentres concentrated between Santorini and Amorgos. The persistent shaking has led to the declaration of a state of emergency, the evacuation of over 11,000 people, and precautionary measures like emptying swimming pools, while emergency crews work to manage potential landslides and structural damage.
What Is a Seismic Swarm?
Unlike a traditional earthquake sequence—where a major quake is followed by smaller aftershocks—a seismic swarm consists of numerous tremors of similar magnitude occurring in rapid succession over a short period.
The name is fitting: much like a swarm of bees or locusts, these quakes appear as a flurry of smaller, closely packed events rather than a single devastating shock.
epa08160262 A local farmer Theophilus Mwendwa tries to chase away a swarm of desert locusts in the bush near Enziu, Kitui County, some 200km east of the capital Nairobi, Kenya, 24 January 2020. Large swarms of desert locusts have been invading Kenya for weeks, after having infested some 70 thousand hectares of land in Somalia which the United Nations Food and Agriculture Organisation (FAO) has termed the ‘worst situation in 25 years’ in the Horn of Africa. FAO cautioned that it poses an ‘unprecedented threat’ to food security and livelihoods in the region. EPA/DAI KUROKAWA
Seismologists first recognized and coined the term in the early to mid-20th century while studying clustered earthquake patterns, particularly in volcanic regions like Japan, Italy, and the United States. Today, the United States Geological Survey (USGS) and other global institutions use the term to classify these events, which are often linked to tectonic shifts, volcanic activity, or underground fluid movements.
What Causes Seismic Swarms?
Several factors can trigger a seismic swarm, including:
- Volcanic Activity – Magma movement underground can destabilize surrounding rock, triggering swarms and sometimes signaling an impending eruption.
- Tectonic Stress Adjustments – Pressure buildup and release along fault lines can lead to repeated earthquakes in a confined area.
- Geothermal & Hydrothermal Systems – The movement of fluids through faults can induce tremors.
- Human-Induced Activity – Activities like fracking, geothermal energy extraction, and reservoir-induced seismicity can contribute to swarm-like behavior.
Because swarms are closely monitored in volcanic regions, their presence near Santorini—a known volcanic hotspot—raises concerns about ongoing tectonic stress beneath the Aegean.
Seismic Swarm in the Cyclades: Latest Developments
With the tremors showing no immediate signs of stopping, authorities have urged residents to take precautionary measures, such as draining swimming pools and avoiding unstable cliffs prone to rockfalls. On 3 February, emergency response teams were deployed to assist with evacuations and structural assessments.
To help monitor this evolving crisis, the European Union’s Copernicus has generated a high-resolution seismic data visualization, leveraging information from the Copernicus Digital Elevation Model. This tool precisely maps earthquake epicentres and magnitudes, offering invaluable insights for scientists and emergency responders.
Why This Matters
Seismic swarms may not always result in a catastrophic event, but they demand close attention, particularly in a geologically active region like the Cyclades.
