Seismic Swarm S20100616.1: Analysis of Earthquake Activity in Greece

Seismic swarm S20100616.1 occurred in Greece from 00:06 on 16 June 2010 to 10:42 on 19 June 2010. Over 82 hours and 36 minutes, the event sequence registered 67 earthquakes. This swarm provides a clear example of clustered seismic activity typical in tectonically active regions.

The sequence began with a magnitude 1.2 event at 9 km depth. Magnitudes increased progressively, peaking at 3.8 on 16 June at 23:00:32 (2 km depth). Multiple events exceeded magnitude 2.5, including several at 3.4. Depths remained shallow, predominantly between 5 km and 10 km, with occasional shallower occurrences near 2–3 km. Activity showed clusters on 16 and 17 June, followed by a decline on 18 and 19 June, ending with a magnitude 2.7 event at 8 km depth.

Greece lies at the boundary between the African and Eurasian tectonic plates. The Hellenic subduction zone drives frequent seismicity across the region, producing both shallow crustal events and deeper earthquakes along the arc. The country experiences hundreds of earthquakes annually, many of low to moderate magnitude. Shallow depths in this swarm align with typical crustal faulting patterns observed in central and southern Greece.

Historical records indicate 15 swarms in Greece since 1 January 2000. Earlier episodes included two in 2008, seven in 2009, and six in 2010 prior to S20100616.1. Such recurrent swarms reflect ongoing stress accumulation and release along active fault systems without a single dominant mainshock.

Analysis of timing and magnitude distribution reveals a classic swarm pattern: gradual onset, multiple comparable events, and no clear foreshock-mainshock-aftershock progression. The concentration of events within the first 48 hours, followed by tapering activity, matches documented behavior in similar Hellenic settings. Depths clustered near 5–10 km suggest involvement of upper crustal structures.

This swarm underscores the value of continuous monitoring for distinguishing swarm sequences from larger tectonic events. Data from the sequence contribute to refined models of strain release in Greece’s complex tectonic environment.

References

• Hellenic Seismic Network bulletins (2010 records)
• European-Mediterranean Seismological Centre historical catalogue
• USGS Earthquake Hazards Program regional summaries