Seismic Swarm S20200223.1: Turkey-Iran Border Region Analysis

The Turkey-Iran border region experienced seismic swarm S20200223.1 between 00:00 on 23 February 2020 and 23:46 on 29 February 2020. In 167 hours and 46 minutes, 189 earthquakes were recorded. Analysis of the first 100 events reveals a concentrated sequence of shallow crustal activity, with magnitudes ranging from 2.0 to 6.0 and focal depths predominantly between 2 km and 20 km. Depths clustered around 7–10 km for the majority of events, indicating activity within the upper crust.

The sequence began with a magnitude 2.5 event at 5 km depth, followed rapidly by a magnitude 5.8 shock at 10 km. Subsequent activity included multiple events above magnitude 4.0 within the first 24 hours, peaking with a magnitude 6.0 earthquake at 10 km depth on 23 February at 16:00:31 UTC. Event frequency was highest in the initial hours, with numerous magnitude 3+ shocks occurring in clusters. Magnitudes above 4.0 accounted for roughly 15 percent of the first 100 events, while the bulk fell between 2.0 and 3.5. Depths remained consistently shallow, rarely exceeding 10 km after the first day.

This swarm occurred within the tectonically complex collision zone between the Arabian and Eurasian plates. The region forms part of the Alpine-Himalayan belt, where ongoing convergence produces both thrust and strike-slip faulting along structures such as the Main Recent Fault and associated splays. Historical seismicity includes destructive events such as the 2017 magnitude 7.3 Iran-Iraq border earthquake and earlier shocks in the 1990s near the same latitude. Updated tectonic models confirm continued strain accumulation at rates of approximately 20–25 mm per year across the plate boundary.

The temporal pattern of S20200223.1, featuring repeated moderate events without a single dominant mainshock followed by clear aftershock decay, aligns with swarm behavior driven by fluid migration or aseismic slip rather than classic aftershock sequences. Depths indicate rupture within brittle upper-crustal layers typical of the Zagros and Anatolian transition zones. No events in the analyzed subset exceeded 20 km depth, consistent with the regional seismogenic thickness.

The swarm underscores the persistent seismic hazard along this international border, where population centers in both countries remain exposed to moderate-to-large events. Continued monitoring is essential given the area’s documented recurrence of clustered activity.

References

SeismoSight internal classification for swarm S20200223.1 (first 100 events data).
USGS Earthquake Hazards Program regional tectonic summaries (2020–2023 updates).
International Seismological Centre bulletin for Turkey-Iran border events.