Seismic Swarm in the Kermadec Islands Region: Analysis of the May 2024 Event

The Kermadec Islands region lies along the Kermadec-Tonga subduction zone, where the Pacific Plate descends beneath the Australian Plate at rates exceeding 6 cm per year. This tectonic setting produces frequent seismic activity, including earthquake swarms, as stresses accumulate and release along the megathrust and associated faults. The islands themselves form part of an intra-oceanic arc characterized by active volcanism and deep seismicity extending to depths greater than 600 km.

On 31 May 2024, a seismic swarm designated PS20240531.1 was recorded in the Kermadec Islands region. The sequence began at 15:54 UTC and concluded at 23:35 UTC, spanning 7 hours and 40 minutes. Five earthquakes were detected during this interval, with magnitudes ranging from 4.7 to 6.2 and focal depths between 10 km and 37 km. The largest event, a magnitude 6.2 earthquake at 16 km depth, initiated the swarm. Subsequent events included a magnitude 5.1 at 10 km, a magnitude 5.2 at 30 km, and two closely spaced shocks of magnitudes 4.7 and 5.0 at depths of 10 km and 37 km, respectively. Such swarms typically reflect fluid migration or aseismic slip triggering brittle failure on adjacent fault segments within the subduction interface.

Historical records since 2000 indicate 33 swarms in the region, with notable clusters in 2021 (10 events) and earlier years including 2003, 2006, 2008, 2014, and 2022–2023. These episodes underscore the persistent seismic productivity of the arc. Strong earthquakes have also punctuated the record, including the magnitude 8.1 event of 4 March 2021 located 46 km from the 2024 swarm center, a magnitude 7.4 shock on the same day 91 km distant, and additional magnitude 7.4, 7.6, and 7.0 events in 2011 and 2008 within 58–83 km. These larger ruptures demonstrate the capacity for great earthquakes along the subduction zone, often preceded or accompanied by swarm-like foreshock activity.

The May 2024 swarm fits within this pattern of moderate, clustered seismicity that may signal stress redistribution following major events or ongoing plate convergence. Depths predominantly in the upper 40 km align with the seismogenic zone of the megathrust, where frictional locking and episodic slip occur. Continued monitoring is essential given the region’s history of generating tsunamigenic earthquakes.

References

• USGS Earthquake Catalog (2000–2024)
• SeismoSight internal swarm classification data