M 8.1; 2021 Kermadec Islands, New Zealand Earthquake; (4 Mar 2021) (50km from the swarm center)
M 7.4; Kermadec Islands, New Zealand; (4 Mar 2021) (64km from the swarm center)
M 7.3; Kermadec Islands, New Zealand; (15 Jun 2019) (82km from the swarm center)
M 7.0; Kermadec Islands, New Zealand; (29 Sep 2008) (49km from the swarm center)
Seismic Swarm PS20140623.1: Kermadec Islands, New Zealand
A seismic swarm designated PS20140623.1 was recorded in the Kermadec Islands region of New Zealand beginning at 19:19 on 23 June 2014 and concluding at 20:07 on 24 June 2014. Over this 24-hour and 48-minute period, 27 earthquakes were registered. The sequence opened with a magnitude 6.9 event at 20 km depth, followed within minutes by a magnitude 6.5 shock at 10 km. A magnitude 6.7 event at 26 km occurred shortly afterward, accompanied by multiple magnitude 5.0–5.9 aftershocks clustered primarily between 4 km and 60 km depth. Later activity included repeated events near 10 km depth, with the final recorded shock reaching magnitude 5.0 at 11 km.
The Kermadec Islands occupy the northern segment of the Tonga-Kermadec subduction system, where the Pacific Plate descends beneath the Australian Plate along the Kermadec Trench. This convergent margin produces frequent seismic swarms and large thrust earthquakes due to ongoing plate convergence at rates exceeding 6 cm per year. The 2014 swarm occurred within the upper plate and along the subduction interface, consistent with the region’s established pattern of clustered intermediate-depth and shallow seismicity.
Since 1 January 2000, ten comparable swarms have been documented in the same area, occurring in 2003 (two events), 2005 (one), 2006 (two), 2008 (three), 2011 (one), and 2012 (one). These episodes reflect episodic stress release along the subduction zone. The 2014 swarm was followed by several strong regional earthquakes, including a magnitude 7.0 event in 2008 located 49 km from the swarm centroid, a magnitude 7.3 event in 2019 located 82 km distant, and the magnitude 8.1 and 7.4 doublet of 4 March 2021 located 50 km and 64 km from the 2014 center, respectively. A magnitude 7.1 earthquake struck 42 km away on 24 April 2023.
Collectively, the Kermadec subduction zone remains one of the most seismically active segments of the Pacific Ring of Fire, with swarm activity serving as an indicator of transient stress changes within the plate interface and overlying crust.
References
SeismoSight internal swarm catalogue PS20140623.1
USGS Earthquake Catalog (regional strong events 2000–2023)
Global CMT Project (tectonic setting of Kermadec Trench)