Location:
102 km W of Sabang, Indonesia
Period:
29 Dec 2004 15:50:04 - 1 Jan 2005 10:15:24 (2d 18h 25m)
Volcanoes in 100km radius:
Seulawah Agam(62km)
Earthquakes:
16
5 swarms found nearby.
2004
PS20041226.2(31.9km)
26 Dec
3 days 6 hours
39 earthquakes
PS20050101.2(197.7km)
31 Dec
21 hours
5 earthquakes
2005
PS20050105.1(56.7km)
4 Jan
1 day 6 hours
9 earthquakes
PS20050113.1(65.7km)
12 Jan
18 hours
5 earthquakes
2015
PS20151108.1(142.7km)
8 Nov
21 hours
11 earthquakes
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Seismic Swarm PS20041230.1: Post-Seismic Activity West of Sabang, Indonesia

The seismic swarm designated PS20041230.1 occurred in a tectonically active region 102 km west of Sabang, Indonesia, within the Andaman Sea sector of the Sunda subduction zone. This area marks the convergent boundary where the Indo-Australian Plate subducts beneath the Eurasian Plate along the Sunda Trench, producing frequent seismicity at depths typically ranging from 10 to 50 km. The regional geology features a combination of megathrust faulting and strike-slip structures associated with the Great Sumatran Fault and its offshore extensions.

The swarm initiated at 15:50 on 29 December 2004 and concluded at 10:15 on 1 January 2005, spanning 66 hours and 25 minutes. During this interval, 16 earthquakes were recorded, with magnitudes between 5.1 and 5.9. Depths varied from 10 km to 49 km, indicating activity across both shallow crustal and intermediate-depth portions of the subducting slab.

Event details include:

  • 29 Dec 2004 15:50:04, magnitude 5.1, depth 38 km
  • 29 Dec 2004 18:50:21, magnitude 5.7, depth 47 km
  • 29 Dec 2004 21:12:57, magnitude 5.9, depth 10 km
  • 29 Dec 2004 21:12:59, magnitude 5.6, depth 29 km
  • 30 Dec 2004 03:42:16, magnitude 5.1, depth 19 km
  • 30 Dec 2004 04:27:36, magnitude 5.2, depth 30 km
  • 30 Dec 2004 21:36:01, magnitude 5.4, depth 30 km
  • 30 Dec 2004 23:04:55, magnitude 5.4, depth 33 km
  • 31 Dec 2004 10:58:21, magnitude 5.2, depth 13 km
  • 31 Dec 2004 14:38:45, magnitude 5.8, depth 33 km
  • 31 Dec 2004 14:38:46, magnitude 5.4, depth 49 km
  • 31 Dec 2004 17:48:05, magnitude 5.9, depth 49 km
  • 31 Dec 2004 17:48:05, magnitude 5.6, depth 33 km
  • 1 Jan 2005 04:03:10, magnitude 5.7, depth 36 km
  • 1 Jan 2005 10:15:24, magnitude 5.2, depth 28 km
  • 1 Jan 2005 10:15:24, magnitude 5.3, depth 33 km

This sequence represents the sole swarm recorded in the region since 1 January 2000, with the preceding swarm also occurring in 2004. Such clustered activity is consistent with the elevated post-seismic stress regime following the Mw 9.1–9.3 Sumatra-Andaman earthquake of 26 December 2004, whose rupture extended into the Andaman Sea and triggered widespread aftershock sequences across the subduction interface.

The swarm's temporal distribution shows peak magnitudes on 29 and 31 December, with events distributed across a range of depths that reflect both interplate and intraplate faulting. Depths around 30–49 km align with the Wadati-Benioff zone geometry in this segment of the trench, while shallower events near 10–19 km suggest activation of overlying crustal structures.

References

USGS Earthquake Catalog
Global CMT Catalog
SeismoSight internal swarm classification PS20041230.1