A seismic swarm designated S20170613.1 occurred near the coast of western Turkey, commencing at 16:00 on 12 June 2017 and concluding at 09:40 on 16 June 2017. The sequence lasted 89 hours and 40 minutes and comprised 45 earthquakes. Magnitudes ranged from 2.0 to 3.5, with focal depths predominantly between 1 km and 20 km, indicating shallow crustal activity typical of the region.
The swarm initiated with events of magnitude 2.4 at 3 km depth and 2.5 at 10 km depth within the first hour. Subsequent shocks included a magnitude 3.1 event at 16 km depth late on 12 June and a magnitude 3.4 shock at 9 km depth on 13 June. Peak activity featured a magnitude 3.5 earthquake at 5 km depth on 14 June, followed by additional events up to magnitude 3.1 on 16 June. Depths remained consistently shallow, with many clustered around 10 km, reflecting normal faulting mechanisms common in extensional settings.
Western Turkey lies within the Aegean extensional province, where back-arc spreading driven by the subduction of the African plate beneath the Eurasian plate along the Hellenic Arc produces widespread normal faulting. The region experiences distributed deformation along multiple fault segments, resulting in frequent low-to-moderate magnitude sequences. Historical records document recurrent seismic swarms in this tectonic environment, consistent with the two prior episodes recorded since 2000 in 2008 and 2011.
Such swarms typically arise from fluid migration or aseismic slip along faults rather than mainshock-aftershock sequences. The 2017 event aligns with this pattern, exhibiting a rapid onset, numerous events of similar magnitude, and no dominant mainshock. Shallow depths amplified felt intensities locally despite modest magnitudes.
This swarm underscores the persistent seismic hazard along Turkey’s western margin. Ongoing monitoring by regional networks supports improved characterization of fault behavior and contributes to refined hazard assessments for coastal communities.
USGS Earthquake Catalog
Turkish National Seismic Network Reports
Hellenic Arc Tectonic Studies (peer-reviewed literature)