Seismic Swarm S20100412.1: Analysis of Greece's April 2010 Earthquake Sequence

Greece lies at the convergent boundary between the African and Eurasian tectonic plates, where the Hellenic subduction zone drives intense seismic activity. The region experiences frequent shallow crustal earthquakes due to the ongoing collision and associated faulting in the Aegean Sea area. This tectonic setting has produced a long history of seismic events, including major historical earthquakes that have shaped the landscape and influenced settlement patterns over millennia.

The seismic swarm designated S20100412.1 occurred in Greece between 02:29 on 11 April 2010 and 08:48 on 12 April 2010. Over this 30-hour period, 37 earthquakes were recorded. Magnitudes ranged from 1.2 to 3.0, with the majority of events registering between 2.0 and 2.9. Focal depths remained shallow, spanning 0 to 13 km, consistent with typical activity along active faults in the Hellenic domain.

The sequence began with a magnitude 2.0 event at 8 km depth. Activity intensified through the morning and afternoon of 11 April, featuring multiple events above magnitude 2.5. A notable cluster developed late on 11 April, with several magnitude 2.7 to 3.0 shocks occurring between 23:13 and 23:58. This included three magnitude 3.0 events at depths of 5 to 10 km. Early on 12 April, the swarm maintained a steady rate, with additional magnitude 3.0 events at 00:06 and 01:00, followed by a gradual decline toward the final recorded shock of magnitude 2.5 at 08:48.

These events illustrate classic swarm characteristics: a rapid succession of small to moderate earthquakes without a single dominant mainshock. The tight temporal clustering and limited magnitude range suggest fluid migration or localized stress adjustments along pre-existing faults rather than a large-scale rupture.

Historical records since 2000 indicate 13 such swarms in the region. Earlier episodes occurred in 2008 (two swarms) and 2009 (seven swarms), with four already documented in 2010 prior to this sequence. This pattern underscores the recurrent nature of swarm activity within Greece's dynamic tectonic environment.

Seismic swarms of this type provide valuable data for understanding short-term crustal behavior in subduction-related settings. Continued monitoring supports improved assessment of seismic hazards across the Hellenic arc.