The Dodecanese Islands lie within one of the most seismically active regions of the eastern Mediterranean, shaped by the ongoing convergence of the African and Eurasian tectonic plates along the Hellenic subduction zone. This tectonic setting produces frequent shallow to intermediate-depth earthquakes as the African plate subducts beneath the Aegean plate. The islands, including Kos, Rhodes, and surrounding smaller landmasses, sit atop a complex network of normal and strike-slip faults that accommodate both subduction-related compression and regional extension.
On 13 January 2019, a seismic swarm designated S20190113.1 was recorded in the Dodecanese Islands. The sequence began at 02:50 UTC and concluded at 23:49 UTC, encompassing a total of 32 earthquakes over 20 hours and 58 minutes. Magnitudes ranged from 2.0 to 4.3, with focal depths predominantly between 1 km and 16 km, indicating activity within the upper crust. The largest event reached magnitude 4.3 at 08:27 UTC and originated at a depth of 10 km.
The swarm displayed a typical pattern of clustered, moderate-energy releases without a single dominant mainshock. Early activity included events of magnitude 2.7 and 2.4 within the first five minutes, followed by a gradual increase in frequency and intensity through the morning hours. Peak activity occurred between 05:00 and 09:00 UTC, featuring the strongest shock and several magnitude-3+ events at shallow depths of 1–2 km. Later phases showed a decline in both magnitude and rate, concluding with a magnitude-3.1 event at 23:49 UTC.
Such swarms are characteristic of the Dodecanese region, where fluid migration and stress transfer along fault networks can trigger prolonged sequences rather than isolated large events. Historical records maintained since 2000 indicate five prior swarms in the area, with one occurring in 2007 and four in 2011. These episodes underscore the persistent seismic hazard associated with the Hellenic Arc.
The 2019 swarm produced no reported damage or casualties, consistent with the moderate magnitudes involved. Monitoring by regional seismic networks allows precise tracking of event migration, which can provide insights into fault behavior and potential precursory signals for larger earthquakes.
Seismic swarms in this setting contribute valuable data for refining hazard models. Continued observation remains essential given the proximity of populated islands and the historical occurrence of stronger events along the same tectonic structures.
References:
SeismoSight internal swarm classification database (S20190113.1).
Hellenic Arc tectonic framework, USGS Earthquake Hazards Program.
Aegean seismicity reports, National Observatory of Athens.