Seismic Swarm S20100716.1: Geological Context and Event Analysis in Greece

Seismic swarm S20100716.1 was recorded in Greece between 21:40 on 15 July 2010 and 00:20 on 19 July 2010. Over 74 hours and 40 minutes, the sequence comprised 43 earthquakes, with magnitudes ranging from 1.4 to 2.9 and focal depths between 2 km and 21 km. The majority of events clustered between 5 km and 10 km depth, indicating shallow crustal activity typical of the region.

This swarm exemplifies the clustered seismicity often observed in tectonically active zones. Events occurred in rapid succession, beginning with a magnitude 2.4 shock at 21:40 on 15 July, followed by multiple events on 16 July, including several of magnitude 2.6–2.8. Activity continued at a moderate rate through 17 and 18 July before tapering off with a final magnitude 1.4 event on 19 July. Such patterns reflect fluid migration or stress redistribution along minor faults rather than a single large rupture.

Greece lies at the convergent boundary between the African and Eurasian plates, where the African plate subducts beneath the Aegean microplate along the Hellenic Arc. This subduction drives intense deformation, producing both shallow crustal earthquakes and deeper events associated with the subducting slab. The Hellenic Trench and associated strike-slip faults accommodate the relative motion, resulting in frequent seismic swarms, particularly in the central and southern Aegean. Historical records document elevated swarm activity since 2000, with 18 swarms recorded through 2010, including three in 2008, seven in 2009, and eight in 2010. These episodes underscore the persistent, distributed nature of strain release in the overriding plate.

The 2010 swarm aligns with this tectonic framework, occurring within the shallow seismogenic layer where brittle failure predominates. Magnitudes remained low, consistent with background seismicity levels in the Aegean, where events rarely exceed magnitude 3.0 during swarms unless linked to larger mainshocks. Depths mostly under 10 km suggest involvement of the upper crust, potentially influenced by geothermal or hydrological factors common in the extensional regime of the Aegean.

Ongoing monitoring by regional networks continues to refine understanding of these sequences. The data from S20100716.1 contribute to models of swarm recurrence and help assess long-term seismic hazard in a country where earthquakes have shaped both landscape and history.

References

• Hellenic Arc tectonics: McKenzie, D. (1978). Active tectonics of the Alpine–Himalayan belt. Geophysical Journal International.
• Aegean seismicity overview: Papazachos, B.C. (1999). Distribution of seismic activity in the Aegean and surrounding areas. Bulletin of the Geological Society of Greece.
• Swarm classification records: SeismoSight internal database (2010).