Seismic Swarm S20090110.1: Analysis of Earthquake Activity in Greece

Seismic swarm S20090110.1 occurred in Greece from 02:20 on 10 January 2009 to 15:40 on 13 January 2009. Over 85 hours and 20 minutes, the event registered 45 earthquakes. This swarm represents one of only two such sequences recorded in the region since 1 January 2000, with the preceding swarm taking place in 2008.

The sequence began with low-magnitude events on 10 January, including multiple shocks of magnitude 1.6 at depths between 1 km and 8 km. Activity intensified midday, featuring a magnitude 3.2 earthquake at 8 km depth, followed by events of magnitude 2.7, 2.5, and 2.4 at depths ranging from 6 km to 16 km. Subsequent tremors remained predominantly below magnitude 2.0, with isolated occurrences reaching magnitude 1.8 at depths up to 20 km. On 11 January, two events of magnitude 2.5 and 1.7 occurred at shallow depths of 5 km and 8 km. Activity continued at a reduced rate on 12 and 13 January, concluding with a magnitude 2.6 event at 8 km depth.

Earthquake depths throughout the swarm clustered between 1 km and 20 km, indicating shallow crustal processes. Magnitudes stayed mostly in the 1.0–2.0 range, with only four events exceeding magnitude 2.5. This pattern aligns with typical swarm behavior, where numerous small events occur without a dominant mainshock.

Greece lies within a highly active tectonic zone at the convergent boundary between the African and Eurasian plates. The Hellenic Arc subduction system drives regional seismicity, with the African plate subducting beneath the Aegean plate. This setting produces frequent shallow earthquakes and occasional swarms linked to fluid migration or crustal stress adjustments along faults. Historical records document persistent seismic activity in Greece, including destructive events that have shaped local building codes and monitoring networks.

The 2009 swarm adds to understanding of Greece's seismic patterns, highlighting episodic clusters amid background tectonic strain. Data from SeismoSight classify this sequence internally, underscoring the value of continuous observation for hazard assessment.

References

• Hellenic Arc tectonic framework from established plate boundary studies.
• Greek seismicity records maintained by national monitoring agencies since 2000.
• Swarm parameters from SeismoSight internal classification S20090110.1.