Seismic Swarm PS20171119.1 Near Tadine, New Caledonia: November 2017 Analysis

New Caledonia lies in a tectonically active zone at the convergent boundary between the Australian and Pacific plates. The Loyalty Islands, including the area around Tadine on Maré Island, experience recurrent seismicity driven by subduction processes along regional trenches. This setting produces both isolated large earthquakes and clustered swarm activity.

Swarm PS20171119.1 began at 09:25 on 19 November 2017 and concluded at 02:20 on 20 November 2017. Over 16 hours and 55 minutes, 21 earthquakes were recorded approximately 20 km south-southeast of Tadine. Magnitudes ranged from 4.3 to 7.0, with focal depths between 5 km and 16 km. The sequence included three events of magnitude 6.0 or greater: a 6.3 at 09:25, a 6.6 at 15:09, and a 7.0 at 22:43 on 19 November, followed by a 6.0 at 00:09 on 20 November.

The temporal distribution showed initial moderate events, followed by a peak in activity during the afternoon and evening of 19 November, with magnitudes generally decreasing after the mainshock. Depths remained shallow throughout, consistent with crustal deformation in the overriding plate.

Since 1 January 2000, twenty seismic swarms have occurred in the broader region. These events cluster in specific years: one each in 2001, 2003, 2004, 2006, and 2015; two each in 2005 and 2008; three each in 2011 and 2017; and four in 2007. Swarm PS20171119.1 was the third recorded in 2017.

Strong earthquakes have also struck nearby since 2000. A magnitude 7.0 event occurred 85 km east-northeast of Tadine on 19 November 2017, only 6 km from the swarm centroid. Additional notable shocks include a magnitude 7.5 on 5 December 2018 located 166 km east-southeast of Tadine and a magnitude 7.0 on 13 January 2011 situated 118 km north-northeast of Tadine.

Such swarm sequences and large events underscore the ongoing seismic hazard in southern New Caledonia. Continued monitoring supports improved understanding of strain accumulation along the plate interface and associated crustal faults.

References
USGS Earthquake Catalog (events 2000–2018)
IRD New Caledonia Seismological Network reports
Global CMT catalog for focal mechanisms and depths