Location:

Period:

22 Mar 2026 06:15:36 - 23 Mar 2026 11:58:52 (1 day 5 hours 43 minutes)

Volcanoes in 100km radius:

Curacoa(75km), West Mata(86km), Tafahi(95km)

Earthquakes:

M 7.0+:

M 8.1; 2009 Samoa Earthquake; (29 Sep 2009) (98km from the swarm center)

9 swarms found nearby.

2004

PS20040904.1(43.7km)

3 Sep

1 day 8 hours

6 earthquakes

2007

PS20071102.1(35.5km)

2 Nov

2 hours

5 earthquakes

2009

PS20090306.1(28.7km)

6 Mar

13 hours

5 earthquakes

PS20090929.1(60.5km)

29 Sep

2 days 19 hours

35 earthquakes

PS20090929.4(40.4km)

29 Sep

5 hours

11 earthquakes

PS20090929.2(78.9km)

29 Sep

6 hours

7 earthquakes

PS20091004.1(91.9km)

4 Oct

1 day 0 hours

6 earthquakes

2015

PS20150330.2(8.8km)

30 Mar

10 hours

6 earthquakes

2017

PS20171104.2(47.1km)

4 Nov

7 hours

5 earthquakes

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Seismic Swarm PS20260322.1: Analysis of Recent Activity Northeast of Hihifo, Tonga

A seismic swarm designated PS20260322.1 was recorded 136 km northeast of Hihifo, Tonga, beginning at 06:15 on 22 March 2026 and concluding at 11:58 on 23 March 2026. Over 29 hours and 43 minutes, the sequence included eight earthquakes with magnitudes ranging from 5.1 to 6.3, all occurring at shallow depths between 9 and 13 km. The events clustered tightly in time, with the strongest activity concentrated on 22 March, including multiple magnitude 6.2 and 6.3 shocks within minutes of each other.

The sequence opened with a magnitude 6.2 event at 06:15:36 on 22 March at 10 km depth. Additional magnitude 6.2 and 6.3 shocks followed later that afternoon at similar depths, succeeded by a magnitude 5.6 event at 16:00:18. Further activity included a magnitude 5.9 event at 22:26:14 on 22 March at 13 km depth, a magnitude 5.8 shock at 06:02:45 on 23 March at 10 km depth, and a final magnitude 5.1 event at 11:58:52 on 23 March at 10 km depth. This pattern reflects typical swarm behavior, characterized by multiple comparable-magnitude events without a single dominant mainshock.

The location lies within the Tonga subduction zone, part of the Pacific Ring of Fire where the Pacific Plate subducts westward beneath the Tonga Plate at rates exceeding 15 cm per year. This tectonic setting produces frequent shallow seismicity along the trench and volcanic arc. The swarm's shallow focal depths align with crustal faulting above the subduction interface.

Historical records since 2000 indicate nine prior swarms in the region, occurring in 2004 (one swarm), 2007 (one swarm), 2009 (five swarms), 2015 (one swarm), and 2017 (one swarm). These episodes demonstrate recurring clustered seismicity without progression to larger mainshock-aftershock sequences. The 29 September 2009 Samoa earthquake of magnitude 8.1, located 98 km from the current swarm center, remains the strongest regional event in the period and triggered widespread tsunami impacts across Samoa, American Samoa, and northern Tonga.

Such swarms contribute to ongoing monitoring of stress accumulation along the subduction interface. Continued observation supports refined hazard assessment in this tectonically active margin.

References:
SeismoSight internal swarm classification PS20260322.1
USGS Earthquake Catalog (historical events since 2000)
Global seismotectonic summaries of the Tonga-Kermadec region