Seismic Swarm Near Rodotópi, Greece, in October 2016

A notable seismic swarm occurred near Rodotópi in the Epirus region of northwestern Greece from 15 to 22 October 2016. Registered as Swarm S20161016.1, the sequence began at 11:48 on 15 October and concluded at 06:39 on 22 October, spanning 162 hours and 51 minutes. During this period, 111 earthquakes were recorded at a location 3 km north of Rodotópi.

The swarm featured a range of magnitudes, with the strongest event reaching 4.9 on 16 October at a depth of 10 km. Multiple events of magnitude 4.3 to 4.8 occurred within the first 48 hours, primarily at depths between 9 and 20 km. Shallower events, some as shallow as 1 km, were also documented, indicating activity across varied crustal levels. Analysis of the first 100 events shows a concentration of higher-magnitude shocks early in the sequence, followed by a gradual decline in both frequency and intensity.

Greece lies at the convergent boundary between the African and Eurasian tectonic plates. In the Epirus region, this interaction involves the subduction of the Ionian oceanic crust beneath the continental margin along the Hellenic Arc. The area belongs to the Ionian geotectonic zone, characterized by thick sedimentary sequences and active thrust faulting. Historical records indicate that Epirus experiences moderate seismicity, often linked to these compressional structures.

According to internal classifications, only one prior swarm has been identified in the region since 1 January 2000, occurring in 2003. This suggests that clustered seismic activity of this type remains infrequent in the immediate vicinity of Rodotópi.

Such swarms typically arise from fluid migration or stress redistribution along existing faults rather than a single large rupture. Depths recorded during the 2016 sequence align with the brittle upper crust in this part of the Hellenides, where earthquakes commonly nucleate between 5 and 20 km.

Ongoing monitoring by national and international networks continues to refine understanding of strain accumulation in northwestern Greece. The 2016 swarm provided valuable data on local fault behavior within a tectonically active setting.

References
SeismoSight internal swarm classification S20161016.1
USGS Earthquake Catalog (Greece regional data)
NOA (National Observatory of Athens) Seismological Bulletin
Scientific literature on Hellenic subduction zone tectonics (post-2016 updates)