Seismic Swarm PS20171104.1 Near Tadine, New Caledonia

Seismic swarm PS20171104.1 occurred on 4 November 2017, approximately 133 km east of Tadine on Maré Island in New Caledonia’s Loyalty Islands. The sequence began at 09:27 UTC and concluded at 21:05 UTC, spanning 11 hours and 38 minutes. During this period, six earthquakes were recorded, with magnitudes ranging from 4.9 to 5.7 and focal depths between 7 km and 15 km.

The events unfolded as follows: a magnitude 5.3 earthquake at 09:27:43 UTC (15 km depth), followed by a magnitude 5.7 event at 14:08:55 UTC (10 km depth), a magnitude 5.4 at 14:52:14 UTC (10 km depth), a magnitude 4.9 at 15:19:00 UTC (10 km depth), a magnitude 5.2 at 15:58:28 UTC (10 km depth), and a final magnitude 5.1 at 21:05:43 UTC (7 km depth). These shallow depths indicate activity within the upper crust, typical of the region’s tectonic environment.

New Caledonia lies at the margin of the Australian and Pacific plates, where the Loyalty Ridge interacts with regional fault systems. This setting produces frequent seismic swarms driven by crustal extension and strike-slip motion rather than direct subduction. The Loyalty Islands, including areas east of Tadine, experience recurrent low-to-moderate magnitude sequences linked to these structures.

Since 1 January 2000, 19 swarms have been documented in the vicinity. These occurred in 2001 (1), 2003 (1), 2004 (1), 2005 (2), 2006 (1), 2007 (4), 2008 (2), 2009 (1), 2011 (3), 2015 (1), 2016 (1), and 2017 (1). Such recurrence underscores the persistent seismic character of the Loyalty Ridge area.

Notable larger events since 2000 include a magnitude 7.0 earthquake on 19 November 2017, located 85 km east-northeast of Tadine and 38 km from the swarm center. A magnitude 7.5 event followed on 5 December 2018, 166 km east-southeast of Tadine and 68 km from the swarm center. Both demonstrate the potential for the region to generate stronger shocks following swarm activity.

This swarm illustrates typical swarm behavior in the Loyalty Islands, where clustered moderate events precede or accompany larger regional earthquakes. Continued monitoring remains essential given the area’s established seismic history.

References
SeismoSight internal swarm classification PS20171104.1 (provided data).
USGS Earthquake Catalog (regional tectonics and event parameters for New Caledonia).
Geoscience Australia (Loyalty Ridge tectonic framework).