An earthquake swarm designated S20111206.1 occurred near the coast of western Turkey between 08:17 on 5 December 2011 and 14:05 on 7 December 2011. Over 53 hours and 48 minutes, the swarm produced 43 events. The sequence began with a magnitude 4.8 earthquake at a depth of 6 km and included events ranging from magnitude 1.5 to 4.8, with the majority occurring at shallow depths between 5 km and 15 km.
The swarm exhibited typical characteristics of clustered seismic activity in an extensional tectonic environment. Initial larger events on 5 December were followed by numerous smaller aftershocks distributed throughout the following two days. Depths remained consistently shallow, consistent with activity along normal faults in the upper crust. No single mainshock dominated the sequence; instead, energy release occurred through repeated moderate events interspersed with lower-magnitude tremors.
Western Turkey lies within the Aegean extensional province, where the Anatolian Plate interacts with the Aegean Plate. This setting produces widespread normal faulting driven by back-arc extension associated with the Hellenic subduction zone to the south. The coastal region experiences frequent small-to-moderate earthquakes due to active graben systems and basin-bounding faults. Historical records document recurrent seismic episodes in this zone, reflecting ongoing crustal stretching at rates of several millimeters per year.
Since 2000, only one prior swarm has been recorded in the same internal classification system, occurring in 2008. The 2011 sequence therefore represents a relatively infrequent clustered event within the broader background of distributed seismicity. Such swarms provide insight into fluid migration or stress triggering along fault networks without producing a single dominant rupture.
The shallow focal depths observed throughout the swarm align with the known seismogenic thickness of the Aegean crust, typically limited to the upper 15–20 km. This pattern supports models of brittle failure in the uppermost crust under extensional stress.
SeismoSight internal swarm classification database.
Regional tectonic summaries from the Turkish Earthquake Foundation and Aegean seismicity studies.