Seismic Swarm S20090303.1: Analysis of March 2009 Events in Greece

Greece lies at the convergent boundary between the African and Eurasian tectonic plates, forming part of the Hellenic subduction zone and the broader Alpine-Himalayan orogenic belt. This tectonic setting produces frequent seismic activity, including both mainshock-aftershock sequences and earthquake swarms. The region experiences shallow crustal earthquakes driven by north-south compression and east-west extension, with many events occurring along active faults in the Aegean Sea and mainland Greece.

Swarm S20090303.1 was recorded between 15:31 on 2 March 2009 and 03:19 on 6 March 2009, spanning 83 hours and 47 minutes. During this interval, 57 earthquakes were detected, with magnitudes ranging from 1.1 to 3.1 and focal depths primarily between 0 and 12 km. The sequence exhibited typical swarm characteristics: a gradual onset, fluctuating event rates without a single dominant mainshock, and a relatively rapid decline in activity.

The initial events on 2 March included low-magnitude shocks at depths of 2–11 km. Activity intensified on 3 March, featuring the largest events of the swarm—a magnitude 3.1 earthquake at 5 km depth at 15:40 and another magnitude 3.1 at 2 km depth at 18:20. Subsequent days showed continued moderate activity, with several events of magnitude 2.6–2.9 recorded through 5 March before the sequence concluded early on 6 March.

This swarm aligns with Greece’s documented pattern of clustered seismicity. Since 1 January 2000, five swarms have occurred in the country, with four recorded in 2008 and one in 2009. Such episodes often reflect fluid migration or aseismic slip along fault zones rather than stress accumulation leading to a larger rupture.

References

• Hellenic Seismic Network bulletins (2009 data)
• USGS Earthquake Catalog – Greece tectonic overview
• European-Mediterranean Seismological Centre regional reports