Seismic Swarm Analysis: Central Turkey, September 2012

An earthquake swarm designated S20120919.1 occurred in central Turkey from 05:58 on 19 September 2012 to 00:41 on 23 September 2012. Over 90 hours and 43 minutes, 92 events were recorded. The sequence featured predominantly shallow foci, with magnitudes ranging from 1.7 to 4.9. The largest event reached M4.9 at a depth of 7 km on 19 September at 09:17:46 UTC. Most events clustered between 5 and 10 km depth, consistent with upper-crustal brittle failure.

The temporal distribution showed peak activity on the first day, including multiple events above M3.0, followed by a gradual decline. Later days recorded fewer and smaller shocks, with the final notable event of M2.1 at 11 km depth on 23 September. Such swarms typically reflect fluid migration or stress redistribution along minor faults rather than a single mainshock-aftershock cascade.

Central Turkey lies within the Anatolian plate, which moves westward relative to the Eurasian and Arabian plates. The region experiences transtensional tectonics influenced by the North Anatolian Fault to the north and the East Anatolian Fault to the southeast. The swarm epicentral area lies near the transition zone between these major strike-slip systems and subsidiary normal faults that accommodate extension in the central Anatolian plateau.

Historical seismicity includes recurrent moderate events along these fault networks. Updated regional records confirm ongoing activity, highlighted by the 6 February 2023 M7.8 Pazarcık earthquake, located 14 km from the 2012 swarm center. That event ruptured a segment of the East Anatolian Fault and formed part of a doublet sequence that caused extensive damage across southeastern Turkey and northern Syria.

The 2012 swarm’s shallow depths and rapid succession align with known patterns of swarm activity in tectonically active zones of central Anatolia. No surface rupture was associated with the sequence, consistent with its modest maximum magnitude. Continued monitoring remains essential given the proximity to major fault structures that have produced large earthquakes in recent years.

References:
United States Geological Survey Earthquake Catalog
Turkish Disaster and Emergency Management Authority (AFAD) seismic bulletins
Active Tectonics of the Mediterranean Region (McKenzie, 1972; updated syntheses)
USGS preliminary report on the 2023 Kahramanmaraş earthquake sequence