Seismic Swarm S20101112.1: Analysis of Activity in Western Turkey

Western Turkey experienced a notable earthquake swarm designated S20101112.1, which commenced at 17:11 on 11 November 2010 and concluded at 10:05 on 20 November 2010. Over 208 hours and 54 minutes, the sequence registered 113 earthquakes. This swarm occurred within a tectonically complex region shaped by the convergence of the Anatolian, Eurasian, and African plates.

The first 100 events revealed predominantly low to moderate magnitudes, with the majority ranging between 2.1 and 3.5. The largest event reached magnitude 5.0 at a depth of 11 km on 11 November at 20:08. Depths remained shallow overall, typically between 0 and 18 km, consistent with crustal faulting in the area. Early activity featured a cluster of events on 11 November, including magnitudes of 4.2 and 3.4, followed by sustained but diminishing seismicity through mid-November. Later events on 18 November showed magnitudes stabilizing around 2.3 to 2.9 at depths of 0 to 16 km.

Western Turkey lies along the western extension of the North Anatolian Fault Zone and within the Aegean extensional domain. The region accommodates right-lateral strike-slip motion along the North Anatolian Fault and north-south extension driven by slab rollback in the Hellenic subduction zone. These processes produce frequent shallow crustal earthquakes. Historical records document major events, such as the 1999 Izmit earthquake of magnitude 7.6, which caused extensive damage along the fault system. The 2010 swarm aligns with background seismicity patterns observed in the area, where swarms often occur without a single dominant mainshock.

Geological mapping indicates that the swarm epicenters fall within zones of active normal and strike-slip faulting associated with the Simav and Gediz grabens. Updated monitoring by regional networks confirms ongoing microseismicity in western Anatolia, reflecting persistent plate boundary deformation. No significant surface rupture was associated with this swarm, typical for events below magnitude 6.

The sequence provides insight into the distributed nature of strain release in the region. Shallow depths suggest activation of upper crustal faults, potentially linked to fluid migration or stress transfer along pre-existing structures. Such swarms contribute to long-term seismic hazard assessment by highlighting areas of elevated activity.

References

• Turkish Republic Disaster and Emergency Management Presidency (AFAD) seismic catalogs
• United States Geological Survey Earthquake Hazards Program
• Geological Survey of Turkey tectonic maps and reports