Location:

Period:

4 Jan 2005 18:26:43 - 6 Jan 2005 00:56:29 (1 day 6 hours 29 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

5 swarms found nearby.

2004

PS20041226.2(71.1km)

26 Dec

3 days 6 hours

39 earthquakes

PS20041226.9(164.9km)

26 Dec

1 day 18 hours

14 earthquakes

PS20041230.1(56.7km)

29 Dec

2 days 18 hours

16 earthquakes

2005

PS20050113.1(14.0km)

12 Jan

18 hours

5 earthquakes

2015

PS20151108.1(106.7km)

8 Nov

21 hours

11 earthquakes

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Seismic Swarm PS20050105.1 Near Banda Aceh, Indonesia

Seismic swarm PS20050105.1 was recorded 63 km west of Banda Aceh, Indonesia, beginning at 18:26 on 4 January 2005 and concluding at 00:56 on 6 January 2005. Over this 30-hour period, nine earthquakes occurred, with magnitudes ranging from 5.2 to 6.2 and focal depths between 8 km and 49 km. The sequence included events at 18:26:43 (magnitude 5.6, 30 km depth), 18:26:44 (5.3, 44 km), 19:08:02 (5.2, 29 km), followed by additional shocks on 5 January at 14:34:31 (5.3, 30 km), 14:34:33 (5.4, 40 km), 14:54:00 (5.7, 8 km), and 14:54:04 (5.9, 48 km). The swarm ended with events on 6 January at 00:56:25 (6.2, 10 km) and 00:56:29 (5.7, 49 km).

This swarm took place in a tectonically active region along the Sunda subduction zone, where the Indo-Australian plate converges with the Eurasian plate at rates of approximately 5–6 cm per year. The area west of Banda Aceh lies near the Sumatran fault system and the trench axis, making it prone to both megathrust and intraslab seismicity. The swarm events cluster at varying depths, consistent with stress redistribution in the overriding and subducting plates.

Banda Aceh, the capital of Aceh Province on northern Sumatra, has a well-documented history of large earthquakes. The 26 December 2004 magnitude 9.1–9.3 megathrust event, centered offshore approximately 250 km to the southwest, produced intense ground shaking and a catastrophic tsunami that devastated coastal communities. The January 2005 swarm occurred shortly afterward, within the aftershock zone of that great earthquake. Historical records indicate three swarms in the region since 1 January 2000, with the first occurring in 2004.

Swarm sequences such as PS20050105.1 differ from typical mainshock-aftershock patterns by lacking a single dominant event and instead featuring closely spaced earthquakes of comparable size. In subduction settings, these clusters may reflect fluid migration along faults, aseismic slip, or triggered failure due to static and dynamic stress changes from prior large ruptures. The 2005 swarm’s temporal proximity to the 2004 megathrust suggests possible triggering, although precise causal links require detailed modeling of Coulomb stress transfer.

Ongoing monitoring by regional and global networks continues to track seismicity in this segment of the subduction zone. Updated catalogs confirm persistent moderate-magnitude activity west of Banda Aceh, underscoring the need for continued preparedness in this high-hazard area.

References

USGS Earthquake Hazards Program – Significant Earthquakes 2004–2005
Global Centroid Moment Tensor Catalog
Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG) regional reports