Location:

Period:

4 Nov 2017 09:00:19 - 4 Nov 2017 16:23:42 (7 hours 23 minutes)

Volcanoes in 100km radius:

West Mata(47km), Curacoa(70km), Niuatahi(80km), Tafahi(97km)

Earthquakes:

9 swarms found nearby.

2004

PS20040904.1(4.1km)

3 Sep

1 day 8 hours

6 earthquakes

2007

PS20071102.1(15.9km)

2 Nov

2 hours

5 earthquakes

2009

PS20090306.1(20.6km)

6 Mar

13 hours

5 earthquakes

PS20090929.1(20.9km)

29 Sep

2 days 19 hours

35 earthquakes

PS20090929.4(55.5km)

29 Sep

5 hours

11 earthquakes

PS20090929.2(122.1km)

29 Sep

6 hours

7 earthquakes

PS20091004.1(121.8km)

4 Oct

1 day 0 hours

6 earthquakes

2015

PS20150330.2(55.9km)

30 Mar

10 hours

6 earthquakes

2026

PS20260322.1(47.1km)

22 Mar

1 day 5 hours

8 earthquakes

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Seismic Swarm PS20171104.2: Analysis of Activity Near Tonga

On 4 November 2017, a seismic swarm designated PS20171104.2 was recorded 110 km NNE of Hihifo, Tonga. The sequence began at 09:00 and concluded at 16:23 local time, encompassing five earthquakes over a duration of 7 hours and 23 minutes. All events occurred at a shallow depth of 10 km, consistent with activity along the shallow portions of the regional subduction interface.

The swarm initiated with a magnitude 6.8 mainshock at 09:00:19. Subsequent events included a magnitude 5.1 earthquake at 12:18:22, a magnitude 5.0 event at 14:36:05, a magnitude 5.6 shock at 15:24:32, and a final magnitude 4.8 earthquake at 16:23:42. This temporal clustering and magnitude distribution illustrate a classic swarm pattern, with the largest event occurring first followed by a rapid decay in size and frequency.

The Tonga region lies within the Tonga-Kermadec subduction zone, where the Pacific Plate converges with and subducts beneath the Tonga Plate at rates exceeding 15 cm per year. This tectonic setting produces frequent shallow seismicity, volcanic arcs, and occasional tsunami-generating events. Historical records indicate persistent seismic productivity, with the 2009 Samoa-Tonga earthquake (magnitude 8.1) highlighting the potential for larger ruptures in adjacent segments.

Swarm activity in the area remains episodic. Since 2000, eight swarms have been documented, occurring in 2004 (one swarm), 2007 (one swarm), 2009 (five swarms), and 2015 (one swarm). These clusters typically reflect transient stress changes along the plate interface or within the overriding plate rather than precursory signals to great earthquakes.

The November 2017 swarm fits this established pattern of short-lived, shallow seismicity. Its limited duration and modest aftershock productivity suggest localized stress release without broader rupture propagation. Continued monitoring of the subduction zone remains essential given Tonga’s position on the Pacific Ring of Fire and its history of generating both seismic and tsunamigenic hazards.

References

SeismoSight internal classification data for swarm PS20171104.2.
USGS Earthquake Catalog for regional tectonic context and historical seismicity in Tonga.
Global CMT catalog entries confirming subduction zone characteristics.