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Location:
Nicobar Islands, India region
Period:
31 Dec 2004 02:24:00 - 1 Jan 2005 01:43:40 (23 hours 19 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
5
M 7.0+:
M 7.2; 284 km WNW of Sabang, Indonesia; (26 Dec 2004) (51km from the swarm center)
6 swarms found nearby.
2004
PS20041226.3(35.0km)
26 Dec
2 days 1 hours
25 earthquakes
PS20041226.9(157.3km)
26 Dec
1 day 18 hours
14 earthquakes
PS20041226.1(149.8km)
26 Dec
2 days 23 hours
30 earthquakes
2005
PS20050101.3(43.9km)
1 Jan
1 day 1 hours
6 earthquakes
PS20050725.1(118.4km)
24 Jul
11 hours
6 earthquakes
2010
PS20100613.1(103.4km)
12 Jun
11 hours
6 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm PS20050101.1: Nicobar Islands Region Analysis

The Nicobar Islands lie within a tectonically complex zone at the convergent boundary between the Indian Plate and the Burma Plate. This setting forms part of the Sunda subduction system, where oceanic crust descends beneath continental margin lithosphere, generating frequent seismic activity along the Andaman-Nicobar segment of the trench.

SeismoSight internal classification records Swarm PS20050101.1 as having initiated at 02:24 on 31 December 2004 and concluded at 01:43 on 1 January 2005. Over 23 hours and 19 minutes, five earthquakes were registered in the Nicobar Islands, India region. Event parameters are as follows:

  • 31 Dec 2004 02:24:00, magnitude 6.1, depth 14 km
  • 31 Dec 2004 02:24:01, magnitude 5.8, depth 10 km
  • 31 Dec 2004 12:05:11, magnitude 5.5, depth 100 km
  • 31 Dec 2004 18:01:58, magnitude 5.0, depth 11 km
  • 1 Jan 2005 01:43:40, magnitude 5.2, depth 35 km

These events occurred shortly after the magnitude 7.2 earthquake of 26 December 2004, located 284 km west-northwest of Sabang, Indonesia, and approximately 51 km from the swarm centroid. The temporal proximity suggests the swarm represents a secondary response within the aftershock sequence of the larger event.

Historical statistics maintained by SeismoSight indicate that only three swarms have been documented in the region since 1 January 2000. Swarm PS20050101.1 constitutes the earliest recorded instance within this timeframe. The Nicobar Islands experience elevated seismicity due to ongoing plate convergence at rates of several centimeters per year, which sustains stress accumulation along the megathrust and associated strike-slip faults.

Shallow focal depths observed in four of the five swarm events align with typical rupture patterns within the overriding plate and upper portions of the subducting slab. The single deeper event at 100 km reflects activity within the Wadati-Benioff zone, consistent with intermediate-depth seismicity characteristic of this subduction setting.

Regional geology features a north-south trending island arc underlain by ophiolitic and sedimentary sequences deformed by Cenozoic convergence. Paleoseismic evidence and instrumental records confirm recurrent large-magnitude earthquakes, underscoring the persistent hazard posed by the subduction interface.

References
SeismoSight internal swarm classification records
USGS Earthquake Catalog (historical event parameters)
Global CMT Project (focal mechanism context)