Seismic Swarm S20130504.2 in Western Turkey: Geological Context and Event Analysis

Western Turkey lies within one of the most tectonically active regions of the eastern Mediterranean, shaped by the convergence of the Eurasian, African, and Arabian plates. The area experiences extensional tectonics associated with the Aegean back-arc system and the westward escape of the Anatolian plate along the North Anatolian Fault. This setting produces frequent shallow crustal earthquakes, with depths typically ranging from 5 to 20 km, consistent with the observed swarm events.

Swarm S20130504.2 was recorded between 17:31 on 3 May 2013 and 13:01 on 5 May 2013, spanning 43 hours and 30 minutes. During this interval, 30 earthquakes were registered in western Turkey. Magnitudes ranged from 1.7 to 3.5, with the largest event reaching 3.5 at a depth of 5 km on 4 May 2013 at 09:10:23. Depths varied between 4 km and 18 km, indicating activity within the upper crust. The sequence began with a 2.1 magnitude event at 5 km depth and concluded with a 2.6 magnitude shock at 5 km depth.

Event timing showed clustering on 3 and 4 May, with multiple events exceeding magnitude 2.5 occurring in the evening of 3 May and midday of 4 May. Notable peaks included three magnitude 3.1 events at depths of 7 km. The distribution of depths suggests a vertically distributed rupture zone typical of swarm activity rather than a single mainshock-aftershock sequence.

Historical records indicate that swarm activity in the region has been limited since 2000. Two prior swarms occurred, one in 2010 and one in 2011. Swarm S20130504.2 represents the third documented swarm in this period, highlighting the episodic nature of clustered seismicity in western Turkey amid ongoing regional extension.

Such swarms are commonly linked to fluid migration or aseismic slip along faults within the Aegean extensional province. The shallow focal depths align with the brittle-ductile transition zone in this tectonically thinned crust. No damage or casualties were associated with this low-to-moderate magnitude sequence.

References

• Turkish National Seismic Network event catalogs (2013 records)
• USGS Earthquake Hazards Program regional tectonics summaries
• McClusky et al. (2000) GPS constraints on Aegean-Anatolian plate motions