Seismic Swarm S20120502.1: Earthquake Activity Near the Western Turkey Coast

Seismic swarm S20120502.1 occurred near the coast of western Turkey between 14:48 on 1 May 2012 and 08:38 on 4 May 2012. In 65 hours and 49 minutes, the sequence produced 61 earthquakes. The events clustered tightly in both time and space, a hallmark of swarm behavior where no single mainshock dominates the energy release. Magnitudes ranged from 1.9 to 4.9, with the largest event recorded at 14:48:28 on 1 May at a depth of 12 km. Subsequent notable shocks included multiple events of magnitude 4.0–4.2 on 2 May at depths between 4 km and 13 km. Depths throughout the swarm varied from 3 km to 17 km, indicating activity within the shallow crust.

Western Turkey lies within the Aegean extensional province, where the Anatolian plate experiences north-south stretching driven by rollback of the Hellenic subduction zone to the south. This tectonic setting produces numerous active normal faults that accommodate extension rates of approximately 20–30 mm per year. The coastal region offshore from western Anatolia is therefore characterized by frequent moderate-magnitude seismicity and occasional seismic swarms. Historical records document repeated earthquake sequences in the same broad area, including notable activity in the early twentieth century and several moderate swarms in the 2000s. These episodes typically last from hours to several days and rarely culminate in destructive mainshocks.

Analysis of the 2012 swarm shows a rapid onset followed by a gradual decline in event rate, consistent with fluid-driven or stress-transfer mechanisms operating along pre-existing faults. The distribution of depths suggests activation of both shallow crustal faults and slightly deeper structures, possibly linked to regional geothermal gradients. No surface rupture or significant damage was associated with the sequence, reflecting the modest maximum magnitude.

The swarm provides a clear illustration of how background tectonic strain in western Turkey is released through clustered rather than isolated events. Continued monitoring by regional networks remains essential for distinguishing such swarms from foreshock sequences that might precede larger earthquakes.

References

• Turkish Disaster and Emergency Management Presidency (AFAD) earthquake catalog
• USGS Earthquake Hazards Program regional reports
• McKenzie, D. (1978). Active tectonics of the Alpine–Himalayan belt. Geophysical Journal International
• Recent syntheses on Aegean extension published in Tectonics (2020–2023 updates)