Earthquake Swarm S20051017.1: Seismic Activity Near the Coast of Western Turkey

The earthquake swarm designated S20051017.1 was recorded near the coast of western Turkey. It began at 04:31 on 17 October 2005 and concluded at 14:08 on 6 November 2005, spanning 489 hours and 37 minutes. During this period, 777 earthquakes were registered.

Analysis of the first 100 events reveals a rapid onset of activity on 17 October, with events distributed across magnitudes from 2.6 to 5.8 and focal depths ranging between 2 and 30 km. The sequence included multiple events above magnitude 4.0 within the initial hours, peaking with a magnitude 5.8 earthquake at 09:46 and a magnitude 5.2 event shortly afterward at 09:55. Subsequent activity showed a mix of smaller tremors, with several clusters of magnitude 3.0–4.4 events occurring through the afternoon and evening. Depths remained predominantly shallow to intermediate, consistent with crustal faulting in the region.

This swarm occurred in western Turkey’s Aegean coastal zone, a tectonically active area shaped by extensional forces. The region forms part of the Western Anatolian Extensional Province, where the Anatolian plate moves westward relative to the Eurasian plate. This motion is driven by the northward collision of the Arabian plate and the rollback of the subducting African slab along the Hellenic Arc. The resulting stress field produces numerous north-south trending normal faults that accommodate east-west extension at rates of approximately 20–30 mm per year.

Seismic history in this sector of the Aegean coast demonstrates recurrent moderate-to-large earthquakes. Notable past events include destructive shocks in the 20th century along coastal fault systems near Izmir and the Gulf of Gökova. The 2005 swarm aligns with this pattern, reflecting episodic release of accumulated strain on segmented normal faults within the upper crust.

The temporal distribution of the initial 100 events indicates swarm-like behavior rather than a classic mainshock-aftershock sequence, with energy release spread across numerous moderate shocks. Depths clustering between 5 and 20 km suggest activation of faults within the seismogenic layer of the continental crust. Such activity underscores the ongoing geodynamic processes that continue to shape the landscape and seismic hazard along Turkey’s western margin.

References:
USGS Earthquake Catalog
Turkish Disaster and Emergency Management Authority (AFAD) seismic records
McKenzie, D. (1978). Active tectonics of the Alpine–Himalayan belt.
Jolivet, L. et al. (2013). Aegean tectonics. Tectonophysics.