Seismic Swarm S20201102.1: Analysis of Western Turkey Activity in November 2020

Western Turkey occupies a highly active tectonic setting at the boundary between the Anatolian Plate and the Aegean extensional domain. The region experiences frequent seismicity driven by north-south extension, strike-slip faulting along the North Anatolian Fault system, and subduction-related processes in the Hellenic Arc to the southwest. Crustal thicknesses average 25–30 km, with shallow brittle failure typical at depths under 15 km. Historical records document destructive events, including the 1999 İzmit earthquake, underscoring the area's long-term seismic hazard.

SeismoSight recorded Swarm S20201102.1 from 05:54 on 1 November 2020 to 11:10 on 7 November 2020, spanning 149 hours and 15 minutes. A total of 153 earthquakes were detected within this period. The first 100 events displayed predominantly low-to-moderate magnitudes, with values ranging from 2.0 to a peak of 4.2. Depths remained shallow, concentrated between 1 km and 16 km, consistent with the regional upper-crustal seismogenic zone.

Activity initiated with a 2.1 event at 14 km depth, followed rapidly by a 2.5 and then the swarm's largest shock of 4.2 at 10 km. Subsequent events clustered in the 2.0–3.5 range, with notable sequences on 2 November and especially late on 3 November, when multiple events above 3.0 occurred within minutes. Magnitudes above 3.5 appeared infrequently, while the majority stayed below 3.0, indicating swarm-like behavior rather than a classic mainshock-aftershock sequence. Depths showed no systematic deepening or migration, remaining stable in the upper 10 km for most events.

This swarm represents the fourth documented swarm in Western Turkey since 2000. Earlier episodes occurred in 2011 and 2013 (one each), with two additional swarms recorded in 2020. The recurrence pattern suggests episodic fluid-driven or stress-transfer processes within the same tectonic corridor.

Collectively, the temporal distribution, magnitude-frequency relationship, and shallow focal depths align with known characteristics of Western Turkey's extensional tectonics. Continued monitoring remains essential given the region's proximity to major population centers and infrastructure.

References: SeismoSight internal swarm classification S20201102.1 USGS Earthquake Catalog (Western Turkey regional tectonics) EMSC Mediterranean seismicity reports