Location:

Period:

12 Jan 2005 13:58:18 - 13 Jan 2005 08:52:43 (18 hours 54 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

5 swarms found nearby.

2004

PS20041226.2(74.5km)

26 Dec

3 days 6 hours

39 earthquakes

PS20041226.9(152.8km)

26 Dec

1 day 18 hours

14 earthquakes

PS20041230.1(65.7km)

29 Dec

2 days 18 hours

16 earthquakes

2005

PS20050105.1(14.0km)

4 Jan

1 day 6 hours

9 earthquakes

2015

PS20151108.1(113.7km)

8 Nov

21 hours

11 earthquakes

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Seismic Swarm PS20050113.1 West of Banda Aceh

Seismic swarm PS20050113.1 occurred approximately 106 km west of Banda Aceh, Indonesia, within the tectonically active Sunda subduction zone. The sequence began at 13:58 on 12 January 2005 and concluded at 08:52 on 13 January 2005, spanning 18 hours and 54 minutes. During this interval, five earthquakes were recorded with magnitudes ranging from 4.7 to 5.7 and focal depths between 29 and 35 km.

The events unfolded as follows: two closely spaced shocks at 13:58:18 and 13:58:19 on 12 January with magnitudes 5.4 and 5.7 at depths of 29 km and 30 km; a 5.1 magnitude event at 18:44:41 that day at 35 km depth; and a final pair at 08:52:40 and 08:52:43 on 13 January with magnitudes 5.7 and 4.7 at 33 km and 30 km. These clustered occurrences reflect typical swarm behavior in which multiple events of similar size take place without a single dominant mainshock.

The location lies along the Sunda megathrust, where the Indo-Australian plate subducts beneath the Eurasian plate at rates of approximately 5–6 cm per year. This convergent margin has produced some of the largest recorded earthquakes, including the magnitude 9.1 event of 26 December 2004 whose rupture extended directly beneath the swarm area. Elevated seismicity in the weeks and months afterward is consistent with post-seismic relaxation and stress redistribution along the plate interface and overlying crustal faults.

Historical records maintained since 1 January 2000 document four swarms in the broader region. Three took place in 2004 and one in 2005, indicating that such episodic clusters form a recurring feature of the subduction zone’s seismic cycle. Swarms of this type often arise from fluid migration or aseismic slip transients that load nearby fault patches, providing insight into the preparatory processes that can precede or follow great earthquakes.

Ongoing monitoring by regional and global networks continues to track microseismicity along the Sunda Trench, improving understanding of strain accumulation and release in this high-hazard corridor.

References

USGS Earthquake Catalog
Global CMT Project
SeismoSight internal swarm classification database