Location:

Period:

4 Jul 2022 08:36:19 - 5 Jul 2022 06:06:13 (21 hours 29 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

11 swarms found nearby.

2004

PS20041226.8(142.3km)

26 Dec

3 days 5 hours

41 earthquakes

PS20041226.5(133.7km)

26 Dec

1 day 11 hours

20 earthquakes

PS20041226.7(49.1km)

26 Dec

11 hours

16 earthquakes

PS20041226.11(197.5km)

26 Dec

13 hours

5 earthquakes

2005

PS20050202.1(37.4km)

1 Feb

14 hours

5 earthquakes

2006

S20060309.1(64.4km)

9 Mar

20 hours

28 earthquakes

PS20060309.1(46.1km)

9 Mar

21 hours

18 earthquakes

S20060310.1(43.9km)

10 Mar

2 days 1 hours

31 earthquakes

2009

PS20090726.1(47.0km)

26 Jul

14 hours

18 earthquakes

2021

PS20210803.1(146.1km)

3 Aug

2 hours

5 earthquakes

2023

PS20230409.1(125.8km)

9 Apr

13 hours

5 earthquakes

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Seismic Swarm PS20220704.1: Analysis of Activity Southeast of Port Blair

A seismic swarm designated PS20220704.1 occurred in the Andaman Sea, approximately 215 km southeast of Port Blair, India. The sequence began at 08:36 on 4 July 2022 and concluded at 06:06 on 5 July 2022, spanning 21 hours and 29 minutes. During this interval, ten earthquakes were recorded, with magnitudes ranging from 4.1 to 5.4 and all events occurring at a focal depth of 10 km. The sequence featured a cluster of five events with magnitude 5.0, alongside a peak magnitude of 5.4 at 00:26 on 5 July.

This swarm exemplifies typical clustered seismicity in a tectonically active subduction environment. Events occurred in rapid succession, particularly on 4 July between 08:36 and 21:24, followed by two final shocks early on 5 July. The consistent shallow depth across all events suggests activity along upper-crustal faults influenced by regional plate interactions.

The Andaman Sea lies within the Sunda subduction zone, where the Indian Plate converges with the Burma Plate at rates of approximately 5–6 cm per year. This oblique subduction drives the formation of the Andaman-Nicobar ridge and associated back-arc spreading centers. The region experiences frequent moderate earthquakes due to both megathrust interface slip and strike-slip faulting along the West Andaman Fault. Historical records indicate elevated swarm activity since 2000, with ten documented swarms occurring in 2004 (four events), 2005 (one), 2006 (three), 2009 (one), and 2021 (one). These clusters often coincide with periods of increased strain release along the arc.

Geological mapping of the area reveals a complex assemblage of oceanic crust, accretionary sediments, and volcanic features shaped by ongoing subduction since the Eocene. The 2004 Mw 9.1 Sumatra-Andaman earthquake, centered nearby, produced widespread co-seismic deformation and triggered aftershock sequences that persisted for years, altering stress patterns in the overriding plate. Subsequent swarms, including the 2022 event, reflect continued adjustment along these fault networks.

Monitoring data from regional seismic networks confirm that such swarms typically lack a single dominant mainshock-aftershock pattern, instead showing distributed energy release over hours to days. Depths near 10 km align with the brittle-ductile transition in this warm subduction setting, where fluids from the downgoing slab may facilitate episodic slip.

References

United States Geological Survey Earthquake Catalog
International Seismological Centre Bulletin
SeismoSight internal swarm classification records