Location:

Period:

31 Mar 2019 23:42:01 - 1 Apr 2019 08:11:32 (8 hours 29 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

16 swarms found nearby.

2004

PS20041226.3(175.8km)

26 Dec

2 days 1 hours

25 earthquakes

PS20041226.5(174.2km)

26 Dec

1 day 11 hours

20 earthquakes

PS20041226.1(195.8km)

26 Dec

2 days 23 hours

30 earthquakes

2005

PS20050101.3(162.2km)

1 Jan

1 day 1 hours

6 earthquakes

S20050127.1(70.7km)

26 Jan

4 days 22 hours

168 earthquakes

S20050127.2(37.9km)

26 Jan

3 days 18 hours

105 earthquakes

PS20050126.1(59.9km)

26 Jan

5 days 20 hours

98 earthquakes

S20050128.1(21.6km)

27 Jan

2 days 5 hours

44 earthquakes

S20050129.1(47.3km)

28 Jan

1 day 12 hours

33 earthquakes

PS20050205.1(81.1km)

4 Feb

2 days 6 hours

10 earthquakes

PS20050216.1(111.2km)

15 Feb

16 hours

5 earthquakes

2014

PS20140321.1(8.2km)

21 Mar

7 hours

7 earthquakes

PS20141111.1(16.7km)

11 Nov

3 hours

5 earthquakes

2015

PS20151108.1(130.5km)

8 Nov

21 hours

11 earthquakes

2021

PS20210803.1(156.3km)

3 Aug

2 hours

5 earthquakes

2023

PS20230409.1(187.2km)

9 Apr

13 hours

5 earthquakes

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Seismic Swarm PS20190401.1 Near Sabang, Indonesia: Geological Context and Event Analysis

A seismic swarm designated PS20190401.1 was recorded 236 km NNW of Sabang, Indonesia, beginning at 23:42 on 31 March 2019 and concluding at 08:11 on 1 April 2019. Over 8 hours and 29 minutes, the sequence comprised 12 earthquakes with magnitudes ranging from 5.0 to 5.5, all at a focal depth of 10 km. The events occurred without a dominant mainshock, consistent with swarm behavior where energy releases in a clustered temporal pattern.

The swarm unfolded as follows: initial activity on 31 March included three events of magnitude 5.0–5.2 between 23:42 and 23:56. On 1 April, nine additional earthquakes took place, peaking with a magnitude 5.5 event at 08:11. Magnitudes remained moderate, with nine events at 5.0, two at 5.1, three at 5.2, and one at 5.5.

This region lies 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 location northwest of Sumatra experiences frequent seismicity due to subduction-related stresses, including both megathrust and intraslab events. Shallow depths around 10 km align with crustal faulting in the overriding plate or outer-rise settings.

Historical records indicate 14 swarms in the area since 1 January 2000, with notable clusters in 2004 (three swarms), 2005 (eight swarms), 2014 (two swarms), and 2015 (one swarm). Such recurrent swarms reflect ongoing tectonic adjustment along the margin, often linked to fluid migration or stress transfer rather than single large ruptures.

The 2019 swarm fits this pattern of episodic moderate-magnitude activity. No significant damage or tsunami risk was associated with these events, given their magnitudes and offshore position. Continued monitoring remains essential in this high-seismicity zone, which has produced great earthquakes historically, including the 2004 Indian Ocean event.

References

USGS Earthquake Catalog
Global CMT Project
SeismoSight internal swarm classification data