Seismic Swarm Analysis: Kermadec Islands Region, January 2022

The Kermadec Islands region forms part of the Kermadec-Tonga subduction zone in the southwestern Pacific Ocean, where the Pacific Plate converges with and subducts beneath the Australian Plate at rates exceeding 6 cm per year. This tectonic setting produces one of Earth’s most seismically active environments, characterized by frequent earthquake swarms, intermediate-depth events, and occasional great earthquakes capable of generating tsunamis. The islands themselves are volcanic edifices built atop the overriding plate, reflecting ongoing arc magmatism driven by slab dehydration. On 29 January 2022, a seismic swarm designated PS20220129.1 was recorded in this region. The sequence began at 02:46 UTC and concluded at 04:59 UTC, lasting 2 hours and 13 minutes. Within that interval, seven earthquakes were detected. The events exhibited the following parameters: a magnitude 6.5 earthquake at 02:46:39 UTC (depth 8 km), followed by magnitude 5.3 at 02:53:25 UTC (10 km), magnitude 5.2 at 03:00:27 UTC (10 km), magnitude 5.3 at 03:01:29 UTC (10 km), magnitude 5.1 at 03:04:51 UTC (10 km), magnitude 5.1 at 04:38:59 UTC (10 km), and a final magnitude 5.8 event at 04:59:10 UTC (10 km). Depths remained shallow to moderate, consistent with upper-plate or interface seismicity typical of the subduction forearc. Such swarms are not uncommon in the Kermadec arc. Since 1 January 2000, twenty-nine swarms have been documented in the broader region. Their temporal distribution includes two in 2003, one in 2005, three in 2006, three in 2008, one each in 2011 and 2012, three in 2014, two in 2016, two in 2019, one in 2020, and ten in 2021. This clustering underscores the episodic nature of stress release along the plate boundary. The 2022 swarm occurred near the epicentral areas of several recent large earthquakes. Notable events since 2000 include a magnitude 7.0 earthquake on 16 March 2023 located 84 km from the swarm center, the magnitude 8.1 Kermadec Islands earthquake of 4 March 2021 situated 47 km away, a magnitude 7.4 event on 21 October 2011 (88 km distant), a magnitude 7.6 shock on 6 July 2011 (46 km distant), and a magnitude 7.0 earthquake on 29 September 2008 (86 km distant). These mainshocks illustrate the region’s capacity for both great subduction-zone ruptures and subsequent aftershock sequences or independent swarms. Continued monitoring of the Kermadec subduction zone remains essential for understanding the interplay between slow slip, swarm activity, and major seismic cycles along this remote plate boundary. References: USGS Earthquake Catalog SeismoSight internal swarm classification PS20220129.1