Seismic Swarm S20070301.1: Insights into Eastern Turkey's February-March 2007 Activity

Eastern Turkey occupies a tectonically active zone within the Alpine-Himalayan orogenic belt, where the northward collision of the Arabian Plate with the Eurasian Plate drives ongoing deformation. This convergence manifests along major structures including the East Anatolian Fault Zone and the Bitlis-Zagros suture, producing frequent shallow crustal earthquakes. The region's geology features complex thrust faults, strike-slip systems, and volcanic provinces shaped by millions of years of compression, resulting in elevated seismic hazard compared to more stable continental interiors.

Seismic swarms represent clusters of earthquakes occurring in rapid succession without a single dominant mainshock, often linked to fluid migration or aseismic slip along faults. Swarm S20070301.1, recorded in Eastern Turkey, exemplifies this pattern. The sequence initiated at 17:53 on 28 February 2007 and concluded at 21:37 on 3 March 2007, spanning 75 hours and 43 minutes. During this interval, 44 earthquakes were registered, with magnitudes ranging from 2.5 to 4.7 and focal depths predominantly between 0 and 30 km, consistent with activity in the upper crust.

The temporal distribution reveals an initial intensification phase on 28 February, featuring events of 3.0, 3.7, and 3.9 magnitude before a peak event of 4.7 at 23:27:45. Subsequent activity on 1–3 March consisted primarily of events below magnitude 3.5, with diminishing frequency toward the sequence's end. Depths remained shallow throughout, averaging under 10 km for most shocks, suggesting involvement of brittle failure in near-surface layers rather than deeper mantle processes.

This swarm aligns with Eastern Turkey's established seismic character. Historical records document recurrent moderate events along regional fault networks, underscoring the area's propensity for clustered seismicity. Since 1 January 2000, two such swarms have been identified, with S20070301.1 representing the first. The concentration of low-to-moderate magnitudes and limited duration distinguishes swarm behavior from typical mainshock-aftershock sequences.

Analysis of event parameters indicates no clear migration of hypocenters, supporting interpretations of localized stress release or hydrothermal influences common in orogenic settings. Depths clustered near 2–8 km for the majority of events further highlight the shallow nature of deformation in this segment of the plate boundary.

References

• SeismoSight internal swarm classification records
• Tectonic framework descriptions from peer-reviewed studies on Arabian-Eurasian plate interaction (e.g., USGS Earthquake Hazards Program summaries)