The Dodecanese Islands lie within the tectonically active Aegean region of Greece, where the convergence of the African and Eurasian plates drives frequent seismic events. This setting features shallow crustal deformation and normal faulting associated with back-arc extension behind the Hellenic subduction zone. The islands have recorded notable historical seismicity, including damaging events in the twentieth century that shaped local building practices and monitoring networks.
Swarm VS20111229.1 began at 13:51 on 28 December 2011 and concluded at 17:48 on 31 December 2011, spanning 75 hours and 56 minutes. During this interval, 110 earthquakes were registered across the Dodecanese Islands. Analysis of the first 100 events reveals predominantly low-magnitude activity, with values ranging from 0.1 to 2.4. Depths remained shallow, concentrated between 0 and 10 km, consistent with upper-crustal processes typical of the region.
Events initiated with magnitudes near 2.0 on 28 December and quickly transitioned to numerous micro-earthquakes below magnitude 1.0. Peak magnitudes of 2.4 occurred on 29 December at depths of 5 km and 9 km. Activity continued through 30 December with similar characteristics, showing clusters of events separated by short quiet periods. The distribution indicates a diffuse swarm pattern rather than a single mainshock-aftershock sequence.
Since 2000, five swarms have been documented in the Dodecanese Islands. Earlier episodes took place in 2007 and 2009, each comprising one swarm, while three swarms were recorded in 2011. This frequency underscores the area's ongoing susceptibility to episodic seismic unrest driven by regional extension.
Such swarms provide valuable data for understanding stress redistribution along local fault systems. Continued monitoring supports improved hazard assessment for the island communities.
SeismoSight internal classification records for swarm VS20111229.1.
Hellenic Seismic Network bulletins on Aegean seismicity.
USGS Earthquake Hazards Program regional tectonic summaries.