Location:

Period:

10 Feb 2021 12:24:21 - 12 Feb 2021 20:55:16 (2 days 8 hours 30 minutes)

Volcanoes in 100km radius:

Hunter Island(95km)

Earthquakes:

M 7.0+:

M 7.7; southeast of the Loyalty Islands; (10 Feb 2021) (19km from the swarm center)

15 swarms found nearby.

2001

PS20010228.1(185.5km)

28 Feb

15 hours

7 earthquakes

2003

PS20030907.1(67.8km)

6 Sep

23 hours

5 earthquakes

2008

PS20081123.1(93.1km)

22 Nov

17 hours

5 earthquakes

2009

PS20090116.1(162.8km)

16 Jan

12 hours

6 earthquakes

PS20090119.1(116.5km)

18 Jan

1 day 10 hours

6 earthquakes

2011

PS20110927.1(46.1km)

27 Sep

1 day 0 hours

8 earthquakes

2016

PS20160812.1(177.0km)

12 Aug

20 hours

7 earthquakes

2018

PS20180829.1(188.8km)

29 Aug

9 hours

7 earthquakes

2021

PS20210203.1(41.1km)

2 Feb

1 hours

8 earthquakes

PS20210214.1(12.0km)

13 Feb

1 day 23 hours

14 earthquakes

2022

PS20220331.1(145.5km)

30 Mar

1 day 16 hours

16 earthquakes

2023

PS20230519.1(106.1km)

19 May

1 day 15 hours

44 earthquakes

S20230519.1(82.9km)

19 May

1 day 22 hours

34 earthquakes

PS20230523.1(121.8km)

22 May

11 hours

6 earthquakes

2026

PS20260713.1(44.0km)

13 Jul

14 hours

6 earthquakes

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Seismic Swarm PS20210210.1 Southeast of the Loyalty Islands

The seismic swarm PS20210210.1 occurred southeast of the Loyalty Islands in the southwestern Pacific Ocean. It began at 12:24 on 10 February 2021 and concluded at 20:55 on 12 February 2021, spanning 56 hours and 30 minutes. During this period, 91 earthquakes were recorded.

The swarm initiated with a magnitude 6.1 event at 12:24 on 10 February at a depth of 11 km. Subsequent activity included multiple events exceeding magnitude 5.0, with peaks at magnitudes 7.7 and 6.3. Depths predominantly ranged between 8 km and 17 km, though isolated deeper events reached 68 km and 80 km. The sequence featured 14 events of magnitude 6.0 or greater, concentrated primarily on 10 February.

This activity aligns with the broader tectonic framework of the region. The Loyalty Islands lie along the Loyalty Ridge, where the Australian Plate interacts with the Pacific Plate near the New Hebrides subduction zone. Subduction-driven compression and associated faulting produce recurrent seismicity, often manifesting as swarms rather than isolated mainshock-aftershock sequences.

Historical records indicate nine such swarms in the area since 1 January 2000. These occurred in 2001, 2003, 2008, 2009 (two swarms), 2011, 2016, 2018, and 2021. The 2021 event included a magnitude 7.7 earthquake located 19 km from the swarm center, consistent with the largest recorded magnitude in the dataset since 2000.

Swarm patterns in this setting typically reflect fluid migration or episodic slip along pre-existing faults within the overriding plate. Depths in the 10–15 km range suggest activation within the upper crust, influenced by the regional stress field from plate convergence rates of approximately 5–7 cm per year.

The February 2021 swarm contributed to ongoing monitoring of seismic hazards in the Loyalty Islands region, where moderate-to-large events remain a characteristic feature of the tectonic environment.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
Geoscience Australia Seismology (ga.gov.au)