Location:

Period:

8 Nov 2015 10:42:01 - 9 Nov 2015 08:12:46 (21 hours 30 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

9 swarms found nearby.

2004

PS20041226.2(169.6km)

26 Dec

3 days 6 hours

39 earthquakes

PS20041226.9(192.8km)

26 Dec

1 day 18 hours

14 earthquakes

PS20041230.1(142.7km)

29 Dec

2 days 18 hours

16 earthquakes

2005

PS20050105.1(106.7km)

4 Jan

1 day 6 hours

9 earthquakes

PS20050113.1(113.7km)

12 Jan

18 hours

5 earthquakes

PS20050126.1(189.8km)

26 Jan

5 days 20 hours

98 earthquakes

2014

PS20140321.1(126.3km)

21 Mar

7 hours

7 earthquakes

PS20141111.1(131.1km)

11 Nov

3 hours

5 earthquakes

2019

PS20190401.1(130.5km)

31 Mar

8 hours

12 earthquakes

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Seismic Swarm PS20151108.1: Earthquake Cluster Analysis Near Sabang, Indonesia

A seismic swarm designated PS20151108.1 was recorded beginning at 10:42 on 8 November 2015 and ending at 08:12 on 9 November 2015. The events occurred approximately 130 km north-northwest of Sabang, Indonesia, in a tectonically active offshore region. In total, 11 earthquakes were registered over 21 hours and 30 minutes.

The sequence began with a magnitude 5.5 event at a depth of 8 km. Subsequent shocks included magnitudes 5.1, 5.2, 5.1, and 4.7, all at depths near 10 km. The largest event reached magnitude 6.6 at 16:47 on 8 November at 10 km depth. Additional events followed with magnitudes 5.2 and 5.6, also at 10 km depth. On 9 November, two magnitude 5.3 events occurred at 06:12, one at 11 km and one at 60 km depth, before the swarm concluded with a magnitude 5.5 shock at 08:12 at 10 km depth.

This swarm reflects typical clustered seismic activity in the region. Most events clustered at shallow depths around 10 km, consistent with crustal faulting, while one deeper event at 60 km suggests limited involvement of the subducting slab.

The area lies along the Sunda subduction zone, where the Indo-Australian Plate converges with and subducts beneath the Eurasian Plate at rates of approximately 5–6 cm per year. This setting produces frequent earthquakes, including great megathrust events and shallower strike-slip activity along the Sumatra Fault System and related structures. Sabang is situated near the northern tip of Sumatra and Weh Island, close to the transition between the Sumatra-Andaman megathrust and the Andaman Sea spreading center.

Historically, the region experienced one of the largest recorded earthquakes, the 2004 Mw 9.1–9.3 Sumatra-Andaman event, which originated roughly 200–300 km to the south-southeast and generated a devastating tsunami. Seismic swarms have occurred intermittently since 2000, with a total of eight documented episodes. Earlier swarms took place in 2004 (three episodes), 2005 (three episodes), and 2014 (two episodes), indicating recurrent episodic clustering without a single dominant causative fault.

Such swarms often result from fluid migration, stress transfer along fault networks, or afterslip following larger regional events. Depths predominantly near 10 km align with the brittle upper crust in this subduction-influenced margin. No significant surface rupture or tsunami was associated with the 2015 swarm.

Ongoing monitoring by regional networks continues to track activity in this high-hazard zone, where convergence sustains elevated seismic risk.

References SeismoSight internal swarm classification database USGS Earthquake Catalog (regional tectonic framework) Global CMT Project (moment tensor solutions for subduction zone events)