Seismic Swarm PS20190519.1 Near New Caledonia: Event Analysis and Regional Context

Seismic swarm PS20190519.1 occurred 192 km east of Tadine, New Caledonia, from 01:23 to 15:06 on 19 May 2019. Within 13 hours and 42 minutes, five earthquakes were recorded, with magnitudes ranging from 4.9 to 6.3 and depths between 10 and 20 km. This sequence exemplifies a typical swarm pattern, featuring clustered events without a dominant mainshock followed by aftershocks.

The five events unfolded as follows: a magnitude 6.3 quake at 20 km depth at 01:23:29, a magnitude 6.0 at 16 km depth at 14:27:11, another magnitude 6.3 at 20 km depth at 14:56:50, a magnitude 5.1 at 10 km depth at 15:01:48, and a magnitude 4.9 at 10 km depth at 15:06:17. Such rapid succession of moderate-to-strong shocks indicates fluid migration or stress transfer along local fault structures in the overriding plate.

New Caledonia lies along the boundary between the Australian and Pacific plates, where oblique convergence drives active tectonics. The region east of the main island aligns with the southern extension of the Vanuatu subduction zone and associated back-arc spreading. Historical records show persistent seismic activity, with 27 swarms documented since 2000. These occurred in the following years and counts: 2001 (1), 2003 (1), 2004 (1), 2005 (2), 2006 (1), 2007 (4), 2008 (3), 2009 (2), 2011 (3), 2015 (1), 2016 (1), 2017 (4), and 2018 (3). Swarm frequency underscores episodic strain release rather than isolated large ruptures.

Strong earthquakes have also punctuated the area since 2000. Notable events include a magnitude 7.0 on 14 September 2022 located 209 km south-southeast of Isangel, Vanuatu (78 km from the swarm center); a magnitude 7.5 on 5 December 2018 located 166 km east-southeast of Tadine (42 km from the swarm center); a magnitude 7.1 on 29 August 2018 located 238 km east-southeast of Tadine (62 km from the swarm center); a magnitude 7.1 on 3 January 2004 located 202 km east-southeast of Tadine (67 km from the swarm center); and a magnitude 7.3 on 27 December 2003 located 201 km east-southeast of Tadine (41 km from the swarm center). Proximity of these events to the 2019 swarm site highlights the persistent seismic hazard along this plate boundary segment.

Swarm activity in this setting often reflects interactions between the subducting Pacific slab and overlying crustal faults. Depths of 10–20 km place the 2019 events within the brittle upper crust, consistent with regional focal mechanisms that show a mix of thrust and strike-slip motion. Continued monitoring remains essential given the historical recurrence of both swarms and larger earthquakes.

References SeismoSight internal classification data for swarm PS20190519.1 and historical statistics. USGS Earthquake Catalog for regional strong-event parameters and plate-boundary context.