Seismic Swarm S20100121.1 in Greece: January 2010 Event Overview
Greece occupies a highly active tectonic setting at the convergent boundary between the African and Eurasian plates. The Hellenic Arc, a major subduction zone, drives frequent seismicity across the region, with shallow crustal events common due to extensional faulting in the Aegean Sea and surrounding areas. This geological framework has produced numerous earthquake swarms throughout recorded history, reflecting episodic stress release along segmented faults.
The swarm designated S20100121.1 began at 22:43 on 20 January 2010 and concluded at 17:38 on 22 January 2010, spanning 42 hours and 55 minutes. During this interval, 28 earthquakes were recorded across Greece. Event magnitudes ranged from 1.3 to 3.1, with the majority falling between 2.0 and 2.9. Focal depths remained shallow, predominantly between 5 and 10 km, though isolated events reached 1 km and 13 km. The sequence exhibited typical swarm characteristics: a gradual onset without a single dominant mainshock, followed by clustered aftershocks of similar size.
Activity initiated with a magnitude 2.6 event at 8 km depth. Subsequent hours saw multiple events near magnitude 3.0 at depths of 5–10 km, including three separate magnitude 2.9 shocks on 21 January. Lower-magnitude events (1.3–1.9) interspersed throughout, often at comparable shallow depths. The final recorded event measured magnitude 2.1 at 8 km on 22 January. This pattern indicates distributed slip along minor fault segments rather than rupture on a single large structure.
Historical records maintained by SeismoSight document ten swarms in Greece since 1 January 2000. Earlier episodes occurred in 2008 (two swarms) and 2009 (seven swarms), underscoring the recurrent nature of such sequences in the region. These events align with Greece’s long-term seismic history, where swarms frequently accompany background tectonic loading along the Hellenic plate boundary.
The 2010 swarm provides insight into short-term seismic clustering. All events remained below damaging thresholds, yet their spatial and temporal density highlights the value of dense monitoring networks for distinguishing swarms from foreshock sequences. Shallow depths suggest activity within the upper crust, consistent with Aegean extensional tectonics.
References
SeismoSight internal classification records for swarm S20100121.1.
Hellenic National Seismic Network routine bulletins (cross-referenced for regional context).
USGS Earthquake Catalog for Greece tectonic framework (2000–2010 period).