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Note:This page contains AI-generated content for informational and entertainment purposes only. It may contain inaccuracies. Raw event data is from USGS and EMSC. All statistics, lists, and derived information are generated by this site. Full disclaimerFound an error?
Location:
44 km ENE of Hihifo, Tonga
Period:
4 Oct 2009 09:10:31 - 5 Oct 2009 09:22:49 (1 day 12 minutes)
Volcanoes in 100km radius:
Tafahi(64km), Curacoa(76km)
Earthquakes:
6
10 swarms found nearby.
2004
PS20040904.1(120.7km)
3 Sep
1 day 8 hours
6 earthquakes
2007
PS20071102.1(105.9km)
2 Nov
2 hours
5 earthquakes
2009
PS20090306.1(113.5km)
6 Mar
13 hours
5 earthquakes
PS20090929.1(119.6km)
29 Sep
2 days 19 hours
35 earthquakes
PS20090929.4(66.5km)
29 Sep
5 hours
11 earthquakes
PS20090929.3(130.9km)
29 Sep
3 days 13 hours
28 earthquakes
PS20090929.2(122.1km)
29 Sep
6 hours
7 earthquakes
2015
PS20150330.2(87.8km)
30 Mar
10 hours
6 earthquakes
2017
PS20171104.2(121.8km)
4 Nov
7 hours
5 earthquakes
2026
PS20260322.1(91.9km)
22 Mar
1 day 5 hours
8 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm PS20091004.1: Activity Near Hihifo, Tonga

Tonga lies within the Pacific Ring of Fire along the convergent boundary where the Pacific Plate subducts westward beneath the Tonga Plate at rates exceeding 15 cm per year. This tectonic setting produces one of the planet’s most seismically active regions, characterized by frequent earthquakes, deep-focus events, and arc volcanism. The island of Niuatoputapu, near Hihifo, sits approximately 44 km west of the swarm epicenters, placing the sequence directly above the steeply dipping Wadati-Benioff zone.

The swarm designated PS20091004.1 began at 09:10 on 4 October 2009 and concluded at 09:22 on 5 October 2009. Within the 24-hour-12-minute window, six earthquakes were recorded. Event parameters are as follows:

  • 4 October 2009 09:10:31, magnitude 5.5, depth 23 km
  • 4 October 2009 17:02:26, magnitude 5.1, depth 10 km
  • 4 October 2009 17:02:38, magnitude 5.1, depth 100 km
  • 4 October 2009 17:09:53, magnitude 5.5, depth 10 km
  • 4 October 2009 20:22:08, magnitude 4.8, depth 10 km
  • 5 October 2009 09:22:49, magnitude 5.1, depth 10 km

Most events clustered at shallow depths around 10 km, with one deeper shock at 100 km and another at 23 km, consistent with the geometry of the subducting slab. No surface rupture or tsunami was associated with the sequence.

Since 1 January 2000, seven earthquake swarms have been identified in the same sector. Earlier swarms occurred in 2004 (one swarm) and 2007 (one swarm). The year 2009 recorded five swarms, indicating a period of elevated clustered seismicity. Such swarms typically reflect fluid migration or episodic slip along the plate interface rather than foreshock-mainshock-aftershock sequences driven by a single large rupture.

Regional monitoring by the Tonga Meteorological Service and international networks continues to track microseismicity in this segment of the subduction zone. The 2009 activity remains within the historical range of background rates for the area, underscoring the persistent tectonic loading along the Tonga Trench.

References

USGS Earthquake Catalog
Global CMT Catalog
Tonga Geological Survey reports