Seismic Swarm PS20230206.1 Near Nurdağı, Turkey

The seismic swarm designated PS20230206.1 occurred in southeastern Turkey, centered 24 km east-northeast of Nurdağı. Registered between 01:17 on 6 February 2023 and 14:20 on 8 February 2023, the sequence lasted 61 hours and 2 minutes and included 17 earthquakes. This activity unfolded within the tectonically active East Anatolian Fault Zone, a major left-lateral strike-slip boundary separating the Anatolian and Arabian plates.

The swarm began with a magnitude 7.8 event at 01:17:34 on 6 February at a depth of 10 km. Subsequent events followed rapidly, with magnitudes ranging from 5.0 to 6.7 and focal depths between 5 km and 17 km. Notable shocks included a magnitude 6.7 event at 01:28:15 and multiple magnitude 5.0–5.5 earthquakes distributed across the following days. The sequence concluded with a magnitude 5.1 event at 14:20:24 on 8 February at a shallow depth of 5 km. Depths remained predominantly shallow, consistent with the regional crustal structure where brittle failure occurs in the upper 15–20 km.

Geologically, the Nurdağı area lies along the East Anatolian Fault, which accommodates westward extrusion of the Anatolian Plate at rates of approximately 10 mm per year. The fault system transitions from the Bitlis-Zagros collision zone in the east to the Hellenic Arc in the west. Historical records show the region experiences recurrent large earthquakes, with the 2023 sequence representing one of the most energetic episodes since instrumental monitoring began. The swarm's location aligns with mapped segments of the fault that have hosted previous ruptures.

Historical statistics since 2000 indicate eight prior swarms in the vicinity, occurring in 2010 (2 events), 2012 (3 events), 2013 (1 event), 2015 (1 event), and 2017 (1 event). These earlier episodes were smaller in scale and lacked mainshocks exceeding magnitude 6.0. In contrast, the 2023 swarm coincided with two major earthquakes in the broader Kahramanmaraş sequence: a magnitude 7.5 event near Elbistan, 9 km from the swarm center, and the magnitude 7.8 Pazarcık mainshock, 85 km distant. Both events occurred on 6 February 2023 and triggered widespread aftershock activity across the fault network.

The shallow focal depths and rapid succession of events in PS20230206.1 reflect stress transfer along interconnected fault segments. Such swarms provide insight into the fault's segmented behavior and the potential for cascading ruptures in this high-strain-rate environment. Continued monitoring remains essential given the area's position at the junction of multiple plate boundaries.

References
USGS Earthquake Catalog (2023 events)
SeismoSight internal swarm classification PS20230206.1