The Dodecanese Islands lie within the tectonically active Hellenic subduction zone, where the African plate converges with the Eurasian plate at rates of approximately 5–10 mm per year. This setting produces frequent shallow crustal seismicity across the Aegean Sea. The islands themselves form part of a volcanic arc influenced by both subduction-related magmatism and extensional tectonics associated with back-arc spreading.
Between 19:00 UTC on 12 December 2011 and 09:10 UTC on 16 December 2011, a seismic swarm comprising 39 events was recorded in the Dodecanese region. All events were of low to moderate magnitude (maximum 3.0) and occurred at shallow depths between 1 km and 12 km. The sequence began with two events above magnitude 2.0 within the first three minutes, followed by a rapid succession of smaller shocks throughout the night of 12 December. Activity continued at a declining rate over the subsequent three days, with the final event of magnitude 2.2 recorded shortly before the swarm’s termination.
Magnitudes ranged from 0.1 to 3.0, with the majority of events falling between 0.5 and 2.0. Depths clustered predominantly between 2 km and 7 km, consistent with brittle failure in the upper crust of this extensional regime. The temporal distribution showed the highest rate of occurrence during the initial 12 hours, after which event frequency decreased steadily.
Historical records maintained since 2000 indicate that only three swarms have been identified in the same area prior to and including this episode: one each in 2007, 2009, and 2011. The 2011 swarm therefore represents the most recent in this sparse sequence, underscoring the episodic rather than continuous nature of swarm-type activity in the Dodecanese.
Such swarms are characteristic of the region’s complex fault network, where fluid migration and stress transfer along minor faults can trigger prolonged sequences of small-magnitude events without culminating in a larger mainshock. The shallow focal depths observed are typical for Aegean crustal earthquakes and imply limited potential for strong ground shaking at the surface.
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