Seismic Swarm Analysis: Eastern Turkey, March 2017

Eastern Turkey occupies a tectonically active segment of the Alpine-Himalayan orogenic belt, where the Arabian Plate converges northward with the Eurasian Plate at rates of approximately 15–20 mm per year. This collision drives crustal shortening, uplift of the Anatolian Plateau, and distributed deformation along major strike-slip and thrust systems, including the East Anatolian Fault Zone and the Bitlis-Zagros suture. The region exhibits elevated seismicity, with shallow crustal earthquakes reflecting both strike-slip motion and reverse faulting in a compressional regime.

The March 2017 swarm, designated S20170302.1, occurred within this setting and was recorded over 416 hours and 19 minutes between 11:07 UTC on 2 March and 19:26 UTC on 19 March. A total of 309 earthquakes were detected. The sequence initiated with a magnitude 5.6 event at 10 km depth, followed by a dense cluster of aftershocks whose first 100 events are examined here.

Analysis of these initial events reveals a classic mainshock-aftershock pattern dominated by shallow foci. Depths ranged predominantly between 5 km and 28 km, with the majority clustered between 7 km and 22 km, consistent with brittle failure in the upper crust. Magnitudes spanned 2.0 to 5.6, with 12 events exceeding magnitude 3.0. The largest aftershocks reached 4.3, 4.0, 3.9, and 3.8, occurring within the first 36 hours. Temporal distribution showed the highest rate in the initial 12 hours, followed by a gradual decay, although secondary bursts of activity persisted through 3 March.

The spatial concentration of events at depths less than 15 km suggests rupture on a relatively small fault segment or distributed fracturing within a heterogeneous crustal volume. Such swarms are not uncommon in Eastern Turkey, where inherited structures from the Arabia-Eurasia collision facilitate fluid migration and stress transfer that can prolong seismic sequences without a single dominant mainshock.

Historically, the same tectonic framework has produced destructive earthquakes, including the 2011 Van sequence and earlier events along the East Anatolian Fault. The 2017 swarm fits within this continuum of moderate-magnitude, shallow activity that contributes to long-term strain accommodation across the plateau.

In summary, the S20170302.1 swarm illustrates the ongoing seismic hazard of Eastern Turkey’s convergent margin. Its rapid onset, shallow depth distribution, and aftershock productivity underscore the importance of continuous monitoring for hazard assessment in this rapidly deforming region.

References

USGS Earthquake Catalog
SeismoSight internal swarm classification S20170302.1