Seismic Swarm PS20080810.1: Analysis of Activity Southwest of Bamboo Flat

On 10 August 2008, a seismic swarm designated PS20080810.1 occurred 146 km southwest of Bamboo Flat, India. The sequence began at 08:20 and concluded at 13:36 local time, encompassing five earthquakes within a span of five hours and fifteen minutes. This event represents one of four documented swarms in the region since 1 January 2000, following earlier clusters in 2004 (two swarms), 2005 (one swarm), and the present 2008 occurrence.

The individual events within the swarm exhibited the following parameters. The initial earthquake at 08:20:33 registered a magnitude of 6.2 at a depth of 20 km. A subsequent event at 09:27:57 reached magnitude 5.3 at 29 km depth. At 12:21:11, a magnitude 5.7 quake occurred at 13 km depth. This was followed by a magnitude 5.3 event at 13:01:31 at 10 km depth. The final earthquake at 13:36:01 measured magnitude 4.2 at 10 km depth. Depths remained relatively shallow throughout, consistent with activity near the plate interface.

The Andaman region lies along the convergent boundary where the Indian Plate subducts beneath the Burma Plate at rates of approximately 5–6 cm per year. This tectonic setting produces frequent seismic activity, including both large megathrust events and smaller clustered swarms. The Andaman-Nicobar Islands form part of an accretionary complex resulting from long-term subduction, with the trench located to the west. Shallow crustal faults and volcanic features further contribute to the area's seismicity.

Historical records indicate elevated activity following the magnitude 9.1–9.3 Sumatra-Andaman earthquake of 26 December 2004, which ruptured a substantial segment of the subduction zone and triggered widespread aftershocks across the Andaman Sea. Subsequent swarms in 2004 and 2005 align with post-seismic relaxation and stress redistribution in the overriding plate. The 2008 swarm occurred in a similar offshore setting, highlighting the persistence of clustered seismicity in this subduction environment.

Such swarms provide insight into transient stress changes along the plate boundary. The concentration of events over several hours, with magnitudes between 4.2 and 6.2, suggests localized fault slip rather than a single mainshock-aftershock sequence. Continued monitoring of the Andaman subduction zone remains essential for understanding long-term seismic hazards in the northeastern Indian Ocean.