Seismic Swarm S20250106.2 in Southern Greece

A seismic swarm designated S20250106.2 occurred in southern Greece from 08:11 on 6 January 2025 to 04:40 on 12 January 2025. Over 140 hours and 28 minutes, the sequence produced 117 earthquakes. Analysis of the first 100 events reveals predominantly low-magnitude activity clustered at shallow depths.

The sequence began with a 2.1-magnitude event at 5 km depth, followed rapidly by additional tremors. Magnitudes ranged mostly between 2.0 and 3.3, with one outlier reaching 4.9 at 10 km depth early on 6 January. Depths remained shallow, concentrated between 0 and 14 km, consistent with crustal faulting in the region. Activity peaked in the initial hours and gradually declined, with events distributed across the six-day period.

Southern Greece lies within the Hellenic subduction zone, where the African plate converges with the Eurasian plate at rates of approximately 30–40 mm per year. This tectonic setting generates frequent seismicity along the Hellenic Arc, including normal, strike-slip, and thrust faulting. The area experiences both large subduction-related events and shallower crustal earthquakes driven by extensional tectonics in the overriding plate.

Historical records indicate that seismic swarms are infrequent in this sector. Since 2000, only one prior swarm has been documented, occurring in 2018. Broader regional history includes destructive earthquakes such as the 365 AD event near Crete and multiple 20th-century shocks, underscoring the persistent seismic hazard.

The 2025 swarm’s characteristics—high event count, modest magnitudes, and shallow foci—align with fluid-driven or stress-transfer mechanisms often observed in subduction-related swarms. No events exceeded magnitude 5.0, suggesting limited potential for significant damage, though the sequence contributed to ongoing monitoring of the Hellenic Arc.

References
SeismoSight internal swarm classification S20250106.2
USGS Earthquake Catalog (regional Hellenic Arc data)
Hellenic Seismic Network bulletins (2025 updates)