Seismic Swarm PS20220110.1: Activity South of the Kermadec Islands

On 10 January 2022, a seismic swarm designated PS20220110.1 was recorded south of the Kermadec Islands. The sequence began at 00:06 UTC and concluded at 06:26 UTC, encompassing a total of six earthquakes over approximately six hours and twenty minutes. This event occurred within the tectonically active Kermadec-Tonga subduction zone, where the Pacific Plate subducts westward beneath the Australian Plate at rates exceeding 6 cm per year. The region features the Kermadec Trench, one of the deepest oceanic trenches, reaching depths beyond 10,000 meters, and is associated with frequent moderate to large earthquakes as well as volcanic arcs.

The swarm initiated with a magnitude 6.2 earthquake at a shallow depth of 7 km, followed within minutes by a magnitude 5.3 event at 10 km depth. Subsequent shocks included two magnitude 5.2 events at 10 km, a magnitude 4.6 event at 10 km, and a final magnitude 5.3 event at 10 km, all clustered in a compact spatial area. Such swarms typically reflect stress adjustments along the subduction interface or within the overriding plate, often without a single dominant mainshock-aftershock pattern.

Geologically, the Kermadec Islands represent emergent portions of the intra-oceanic Kermadec Arc, formed through prolonged subduction-related magmatism. Historical records indicate elevated seismicity in this segment, with notable large events including the 1976 magnitude 8.0 earthquake and the 2011 magnitude 7.6 event, both linked to thrust faulting on the plate boundary. Updated monitoring from global seismic networks confirms ongoing background activity consistent with the arc's position in the Pacific Ring of Fire.

Historical analysis of swarm-type sequences in the area since 2000 reveals three prior episodes: one in 2001, one in 2005, and one in 2020. The 2022 swarm adds to this sparse but recurring pattern, highlighting episodic clustering that may relate to fluid migration or aseismic slip transients along the megathrust. Depths predominantly near 10 km suggest activity within the upper portion of the subducting slab or the plate interface.

Seismic swarms in subduction settings like this provide valuable data for understanding strain accumulation and release. Continued observation through regional networks aids in refining hazard assessments for nearby island chains and coastal areas of New Zealand, which lie along the same tectonic system to the south.

References

• USGS Earthquake Catalog (earthquake.usgs.gov)
• GNS Science New Zealand seismic reports
• International Seismological Centre event bulletins