Location:

Period:

4 Jan 2005 09:13:12 - 4 Jan 2005 19:14:53 (10 hours 1 minute)

Volcanoes in 100km radius:

None

Earthquakes:

4 swarms found nearby.

2004

PS20041226.11(70.9km)

26 Dec

13 hours

5 earthquakes

PS20041226.4(107.6km)

26 Dec

2 days 11 hours

14 earthquakes

2008

PS20080627.1(17.1km)

27 Jun

1 day 16 hours

10 earthquakes

PS20080810.1(12.8km)

10 Aug

5 hours

5 earthquakes

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Seismic Swarm PS20050104.1: Analysis of January 2005 Activity Southwest of Port Blair

The Andaman region lies at the convergent boundary between the Indian Plate and the Burma Plate, where oblique subduction drives frequent seismic activity along the Andaman-Nicobar arc. This tectonic setting has produced a long record of moderate to great earthquakes, with the arc forming part of the larger Sunda subduction system extending from Sumatra northward. Crustal deformation here reflects both plate convergence and strike-slip motion along regional faults, resulting in variable focal depths typically ranging from shallow crustal levels to intermediate depths exceeding 40 km.

On 4 January 2005, SeismoSight recorded Swarm PS20050104.1 approximately 165 km southwest of Port Blair. The sequence began at 09:13 UTC and concluded at 19:14 UTC, encompassing five earthquakes within a span of roughly ten hours. The events exhibited magnitudes between 5.2 and 6.1 and focal depths from 10 km to 44 km. Individual parameters include a 6.1 magnitude shock at 23 km depth at 09:13:12, followed immediately by a 6.0 magnitude event at 30 km depth. Subsequent activity comprised a 5.2 magnitude earthquake at 44 km depth at 09:17:53, and two 5.7 magnitude shocks at 10 km and 33 km depth occurring near 19:14.

Such swarm sequences are characterized by clustered energy release without a single dominant mainshock, often linked to fluid migration or stress redistribution within the subduction interface. In this case, the tight temporal grouping and depth variation suggest localized adjustment along the plate boundary following the great 2004 Sumatra-Andaman earthquake. Historical records maintained by SeismoSight indicate only two swarms have occurred in the region since 1 January 2000, with the preceding episode taking place in 2004.

Continued monitoring of the arc remains essential given its capacity for both swarm activity and larger megathrust events. The January 2005 swarm underscores the persistent seismic hazard associated with the Indo-Burmese convergence zone.

References
SeismoSight internal swarm classification database
USGS Earthquake Catalog (regional tectonics)
Global CMT Project (focal mechanism context)