Seismic Swarm S20230725.1 in Central Turkey: July 2023 Overview

Central Turkey occupies a tectonically complex zone within the Anatolian Plate, which moves westward under the combined influence of the northward-advancing Arabian Plate and the relatively stable Eurasian Plate. This motion produces distributed deformation across the region, primarily accommodated by strike-slip fault systems and associated secondary structures. Shallow crustal seismicity is common, with events typically occurring at depths of 1–15 km. The July 2023 swarm occurred in this setting, consistent with the area’s long-term pattern of clustered earthquake activity.

The swarm, internally classified as S20230725.1, began at 05:44 on 25 July 2023 and concluded at 05:11 on 29 July 2023. Over 95 hours and 27 minutes, 69 earthquakes were recorded. The sequence opened with a magnitude 5.5 event at 13 km depth, followed by numerous smaller events whose magnitudes ranged from 1.3 to 4.4. Depths remained predominantly shallow, mostly between 1 and 12 km. The largest subsequent shock reached magnitude 4.4 at 10 km depth on 25 July. Activity declined steadily after the first 48 hours, with only isolated events above magnitude 3.0 recorded on 27 and 28 July. The final event, magnitude 2.0 at 5 km depth, marked the swarm’s termination.

This sequence represents the second swarm documented in central Turkey since 1 January 2000. The preceding swarm occurred in 2010. Both episodes illustrate episodic clustering rather than isolated mainshock–aftershock sequences, a recognized feature of the region’s fault network where fluid migration or aseismic slip may trigger multiple small ruptures.

The 2023 swarm’s temporal evolution shows a classic swarm pattern: an energetic onset, rapid rate of smaller events, and gradual decay without a single dominant aftershock. Magnitudes followed a typical Gutenberg–Richter distribution, with the majority below 3.0. Depths clustered around 5 km, suggesting activation of a shallow crustal volume. No surface rupture was reported, consistent with the modest energy release and limited maximum magnitude.

Regional monitoring networks continue to track background seismicity in central Turkey. The 2023 swarm adds to the instrumental record that began with earlier events in 2010, reinforcing the value of dense seismic arrays for distinguishing swarm behavior from classic aftershock sequences.

References
SeismoSight internal swarm classification S20230725.1
USGS Earthquake Catalog – Anatolian Plate tectonics summary (updated 2023)