Location:

Period:

6 Mar 2021 07:16:19 - 7 Mar 2021 02:07:12 (18 hours 50 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.4; Kermadec Islands region; (21 Oct 2011) (72km from the swarm center)

24 swarms found nearby.

2005

PS20050628.1(172.2km)

28 Jun

1 hours

5 earthquakes

PS20050712.1(171.6km)

11 Jul

9 hours

5 earthquakes

2006

PS20060331.1(153.8km)

31 Mar

1 day 8 hours

23 earthquakes

PS20060405.1(123.8km)

4 Apr

1 day 3 hours

10 earthquakes

PS20060501.2(23.2km)

1 May

19 hours

5 earthquakes

2011

PS20110706.1(105.4km)

6 Jul

5 days 11 hours

52 earthquakes

2012

PS20120128.1(140.5km)

28 Jan

2 hours

10 earthquakes

2016

PS20160713.1(47.9km)

13 Jul

14 hours

10 earthquakes

2020

PS20200118.1(98.8km)

18 Jan

17 minutes

5 earthquakes

2021

PS20210304.2(140.0km)

4 Mar

4 days 4 hours

107 earthquakes

PS20210305.1(107.0km)

4 Mar

2 days 13 hours

28 earthquakes

PS20210304.3(187.3km)

4 Mar

1 day 3 hours

21 earthquakes

PS20210316.1(114.9km)

15 Mar

17 hours

5 earthquakes

PS20210406.1(128.4km)

5 Apr

15 hours

6 earthquakes

PS20210407.1(61.7km)

7 Apr

15 hours

9 earthquakes

PS20210427.1(119.7km)

26 Apr

1 day 14 hours

10 earthquakes

PS20210429.1(164.1km)

29 Apr

19 hours

8 earthquakes

PS20210725.1(163.2km)

25 Jul

8 hours

5 earthquakes

2022

PS20220129.1(138.2km)

29 Jan

2 hours

7 earthquakes

PS20220202.1(66.1km)

2 Feb

14 hours

5 earthquakes

2023

PS20230613.1(99.5km)

13 Jun

23 hours

7 earthquakes

2024

PS20240531.1(121.6km)

31 May

7 hours

5 earthquakes

PS20241017.1(59.2km)

16 Oct

17 hours

5 earthquakes

2025

PS20250531.1(163.9km)

31 May

1 day 7 hours

6 earthquakes

AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Earthquake Swarm PS20210306.1 in the Kermadec Islands Region

An earthquake swarm designated PS20210306.1 occurred in the Kermadec Islands region, beginning at 07:16 on 6 March 2021 and concluding at 02:07 on 7 March 2021. Over the 18-hour-and-50-minute period, ten earthquakes were recorded. The events ranged in magnitude from 4.7 to 6.1, with focal depths between 8 and 19 km. The sequence included two events above magnitude 6.0, highlighting a period of elevated seismic activity along this tectonically active margin.

The Kermadec Islands form part of the Kermadec-Tonga subduction zone, where the Pacific Plate subducts westward beneath the Australian Plate at rates exceeding 5 cm per year. This convergent boundary produces frequent shallow to intermediate-depth earthquakes and hosts submarine volcanoes. The swarm’s shallow depths place the activity within the overriding plate or near the plate interface, consistent with stress release in a region of ongoing subduction.

Seismic swarms have occurred periodically in the Kermadec Islands since at least 2000, with twelve documented episodes through 2021. Prior swarms took place in 2005 (two events), 2006 (three), 2011 (one), 2012 (one), 2016 (one), 2020 (one), and three in 2021. These clusters typically involve multiple moderate-magnitude events over hours to days without a single dominant mainshock.

A notable larger earthquake, magnitude 7.4, struck the same region on 21 October 2011, approximately 72 km from the 2021 swarm center. Such events underscore the potential for both swarm activity and isolated strong shocks within this subduction setting.

The 2021 swarm events, listed chronologically, were as follows:

6 March 2021 07:16:19, magnitude 5.6, depth 10 km
6 March 2021 07:16:29, magnitude 6.1, depth 10 km
6 March 2021 12:12:04, magnitude 5.4, depth 10 km
6 March 2021 13:29:48, magnitude 5.0, depth 10 km
6 March 2021 14:28:42, magnitude 4.7, depth 10 km
6 March 2021 17:32:59, magnitude 5.5, depth 19 km
6 March 2021 21:42:50, magnitude 5.2, depth 10 km
6 March 2021 21:47:39, magnitude 5.1, depth 10 km
7 March 2021 01:55:10, magnitude 5.5, depth 8 km
7 March 2021 02:07:12, magnitude 5.2, depth 10 km

Collectively, these data illustrate a typical swarm pattern of closely spaced, moderate-magnitude earthquakes without clear foreshock-mainshock-aftershock progression.

References
USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
SeismoSight internal swarm classification PS20210306.1