Seismic Swarm Near Nurhak, Turkey: February 2023 Analysis

A seismic swarm designated S20230206.4 was recorded 3 km east-southeast of Nurhak in Turkey's Kahramanmaraş Province. The sequence began at 04:04 on 6 February 2023 and concluded at 04:10 on 8 February 2023, spanning 48 hours and 6 minutes. During this interval, 53 earthquakes were registered.

The swarm occurred within a tectonically active corridor shaped by the East Anatolian Fault Zone, a left-lateral strike-slip system that accommodates westward extrusion of the Anatolian Plate relative to the Arabian Plate. Regional geology features Paleozoic metamorphic basement overlain by Mesozoic carbonates and Cenozoic sedimentary-volcanic units, with active faulting concentrated along the main strand of the East Anatolian Fault and subsidiary structures near the Nurhak bend. Focal depths for the swarm events ranged predominantly between 3 km and 24 km, consistent with brittle failure within the upper crust along this fault system.

Key events illustrate the swarm's temporal evolution. The initial shock reached magnitude 4.3 at 22 km depth. Subsequent activity included multiple magnitude 4.6–4.9 events clustered between 10:38 and 13:03 on 6 February, with depths of 9–17 km. Later phases on 7 February featured a magnitude 4.8 event at 10 km depth and a magnitude 4.7 shock at only 3 km depth, indicating shallow crustal involvement. The sequence tapered with smaller events through the early hours of 8 February.

Historical records maintained since 1 January 2000 document only two swarms in the immediate vicinity, with the first occurring in 2023. This rarity underscores the episodic nature of clustered seismicity along the East Anatolian Fault prior to the larger February 2023 mainshock sequence that ruptured the same fault system.

The Nurhak swarm provides insight into precursory fault behavior. Magnitudes remained moderate, with the largest event reaching 4.9, while depths showed a bimodal distribution favoring 5–17 km intervals. Such patterns reflect distributed slip on fault segments under increasing stress, typical of swarm activity in strike-slip regimes rather than classic foreshock-mainshock-aftershock sequences.

References
SeismoSight internal classification data for swarm S20230206.4
USGS Earthquake Catalog and regional tectonic summaries (2023 updates)
Active Fault Map of Turkey, General Directorate of Mineral Research and Exploration (updated 2022)