Seismic Swarm S20200218.1 in Western Turkey: Geological Context and Event Analysis

Western Turkey lies within a tectonically complex region shaped by the interaction of the Eurasian, African, and Arabian plates. The area experiences extensional tectonics driven by slab rollback along the Hellenic subduction zone and westward extrusion of the Anatolian plate along the North Anatolian Fault. This setting produces numerous active normal faults and graben systems, resulting in frequent shallow seismicity at depths typically between 5 and 15 km.

The seismic swarm S20200218.1 was recorded in this environment, commencing at 23:43 on 17 February 2020 and concluding at 03:32 on 3 March 2020. Over 339 hours and 48 minutes, 290 earthquakes were detected. Analysis of the first 100 events reveals predominantly low-to-moderate magnitudes, with the majority ranging from 2.0 to 3.4 and two notable peaks at 4.8 and 4.3. Depths remained shallow, clustering between 5 and 11 km for most events, consistent with the extensional faulting characteristic of the region. Activity intensified on 18 February, with multiple events exceeding magnitude 3.0 occurring within hours, followed by a gradual decline in frequency and intensity through 20 February.

This swarm aligns with patterns observed in prior episodes documented since 2000. Four swarms have occurred in total, with earlier instances in 2016 (two events), 2017 (one event), and the current 2020 sequence. Such swarms often reflect fluid migration or aseismic slip along segmented faults rather than a single large rupture, posing lower immediate hazard but indicating ongoing strain accumulation.

The broader seismic history of Western Turkey includes destructive events linked to the same fault systems, underscoring the need for continued monitoring. Data from this swarm contribute to refined models of local fault behavior and stress transfer in the Aegean extensional province.

References

SeismoSight internal swarm classification records.
USGS Earthquake Catalog for regional tectonic framework.
Peer-reviewed studies on Aegean extensional tectonics (e.g., from Journal of Geophysical Research).