Seismic Swarm S20121114.2 in Central Turkey: Analysis of the November 2012 Sequence

A seismic swarm designated S20121114.2 was recorded in central Turkey between 21:59 on 13 November 2012 and 10:52 on 16 November 2012. Over 60 hours and 53 minutes, 37 earthquakes were registered. The sequence featured a maximum magnitude of 4.5 and occurred at shallow depths, with events clustered between 1 km and 29 km.

The swarm initiated with a magnitude 3.5 event at 6 km depth, followed within hours by a magnitude 4.5 shock at 13 km. A magnitude 4.3 event occurred minutes later at 12 km. Subsequent activity consisted predominantly of events below magnitude 3.0, with occasional moderate shocks reaching 3.2. Depths remained consistently shallow throughout, consistent with upper-crustal faulting in the region.

Central Turkey lies within the Anatolian tectonic plate, bounded by the North Anatolian Fault to the north and the East Anatolian Fault to the southeast. The area experiences distributed deformation due to the westward extrusion of the Anatolian plate driven by the collision between the Arabian and Eurasian plates. Historical seismicity reflects this setting, with frequent moderate events along secondary faults and fracture zones subsidiary to the major strike-slip systems.

Since 1 January 2000, two swarms have been documented in the broader region; the 2012 sequence represents the first. On 6 February 2023, the magnitude 7.8 Pazarcık earthquake occurred as part of the Kahramanmaraş sequence, with its epicenter approximately 14 km from the 2012 swarm center. This event ruptured a significant segment of the East Anatolian Fault and was followed by a magnitude 7.6 aftershock hours later, highlighting the continued seismic potential of the fault network surrounding the earlier swarm.

The 2012 swarm exhibited classic characteristics of clustered seismicity: rapid onset, a mix of foreshock-like larger events, and a long tail of smaller aftershocks decaying over days. No single mainshock dominated; instead, energy release was distributed across multiple events of comparable size. Depths indicate activity within the brittle upper crust, where fluid migration or aseismic slip may have contributed to triggering.

Such swarms provide insight into fault behavior in tectonically active zones. They often occur on immature or secondary structures and can precede or follow larger earthquakes by years, as seen with the 2023 rupture located nearby. Continued monitoring of microseismicity in central Turkey remains essential for understanding stress transfer along the East Anatolian Fault system.

References

USGS Earthquake Catalog (events 2012–2023)
Turkish Disaster and Emergency Management Authority (AFAD) seismic bulletins
Active Tectonics of the Eastern Mediterranean Region, Geological Society of London Special Publications