Seismic Swarm S20100212.1: Analysis of Seismic Activity in Greece

Greece lies at the convergent boundary between the African and Eurasian tectonic plates, where the African plate subducts beneath the Eurasian plate along the Hellenic Arc. This subduction zone drives frequent seismic activity across the region, including shallow crustal events and deeper intermediate-depth earthquakes associated with the subducting slab. The Hellenic Trench and associated fault systems, such as the Corinth Rift and the North Aegean Trough, contribute to the country's high seismicity, with historical records documenting destructive events over centuries. Seismic swarms—clusters of earthquakes occurring in rapid succession without a clear mainshock—represent a notable feature of Greece's tectonic environment. These swarms often reflect fluid migration or stress redistribution along faults rather than large-scale plate motion. Data from SeismoSight indicate that 13 such swarms have occurred since 1 January 2000, with four recorded in 2008, seven in 2009, and two in 2010. Swarm S20100212.1 began at 23:43 on 11 February 2010 and concluded at 21:06 on 20 February 2010, spanning 213 hours and 23 minutes. During this period, 128 earthquakes were registered across Greece. Analysis of the first 100 events reveals predominantly shallow focal depths, with the majority occurring between 1 km and 10 km. Magnitudes ranged from 1.3 to 4.2, clustering most frequently between 2.5 and 2.9. Notable outliers include a magnitude 4.2 event at 39 km depth on 12 February at 19:48 and several magnitude 3.0–3.3 shocks at depths of 5–9 km. Temporal distribution shows peak activity on 12–14 February, with events spaced minutes to hours apart. Depths remained consistently shallow after the initial deeper shock, suggesting activity concentrated in the upper crust. This pattern aligns with fluid-driven swarm behavior common in extensional tectonic settings within Greece. The swarm's characteristics underscore the ongoing monitoring value of dense seismic networks in the region. Continued observation helps refine models of stress accumulation along the Hellenic subduction interface and adjacent fault zones.

References

SeismoSight internal swarm classification records for S20100212.1.
USGS Earthquake Hazards Program summaries of Hellenic Arc tectonics.
Hellenic Seismic Network historical bulletins on regional swarm frequency.