Seismic Swarm S20060310.1: Andaman Sea Earthquake Sequence of March 2006

Seismic swarm S20060310.1 was recorded between 00:14 UTC on 10 March 2006 and 02:13 UTC on 12 March 2006, approximately 203 km southeast of Port Blair in the Andaman Islands, India. Over 49 hours and 58 minutes, the sequence comprised 31 earthquakes, with magnitudes ranging from 4.1 to 5.0 and focal depths between 10 and 25 km. The events clustered tightly in both space and time, characteristic of swarm activity rather than a mainshock-aftershock sequence.

The Andaman Sea region forms part of the Sunda subduction zone, where the Indian Plate converges obliquely with the Burma microplate at rates of 5–6 cm per year. This tectonic setting produces frequent moderate seismicity along the Andaman Trench and associated strike-slip faults. Depths of 10–25 km align with the seismogenic portion of the overriding plate and the shallow megathrust interface. The swarm’s location places it east of the trench axis, within a zone of distributed deformation that includes back-arc spreading centers.

Regional tectonics have been shaped by the great Mw 9.1 Sumatra–Andaman earthquake of 26 December 2004, whose rupture extended northward along the trench into the Andaman segment. That event triggered widespread stress changes, elevating background seismicity for years afterward. Post-2004 data show persistent clusters of moderate events, consistent with the four documented swarms recorded since 2000: one in 2004, one in 2005, and two in 2006. The March 2006 swarm occurred roughly 15 months after the great earthquake, illustrating continued readjustment along the plate boundary.

Individual events within the swarm exhibited magnitudes between 4.1 and 5.0, with several reaching 4.8–5.0 on 10 and 11 March. Depths remained shallow, predominantly 10–25 km, indicating brittle failure within the upper crust and near the plate interface. The absence of a single dominant mainshock and the rapid succession of similar-sized events further support classification as swarm behavior driven by fluid migration or aseismic slip transients.

Such swarms contribute to the long-term seismic energy release in the Andaman segment without producing destructive shaking on nearby islands. Continued monitoring of the subduction zone remains essential given the potential for future large megathrust events.

References
USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
SeismoSight internal swarm classification S20060310.1