Seismic History of the Loyalty Islands, New Caledonia

The Loyalty Islands lie east of the main island of New Caledonia in the southwest Pacific Ocean. This region sits near the convergent boundary between the Australian and Pacific plates, where subduction along the New Hebrides Trench generates frequent large earthquakes. The Loyalty Ridge, an uplifted oceanic feature, forms the islands and experiences ongoing deformation from plate interaction. Instrumental records show repeated magnitude 7 or greater events clustered southeast of the Loyalty Islands. On 27 December 2003, a magnitude 7.3 earthquake struck 201 km east-southeast of Tadine at a depth of approximately 22 km. Six days later, on 3 January 2004, a magnitude 7.1 event occurred at the same location and depth, underscoring the area’s capacity for paired large ruptures. Seismic activity continued in subsequent years. On 29 August 2018, a magnitude 7.1 earthquake was recorded 238 km east-southeast of Tadine. Roughly three months later, on 5 December 2018, a magnitude 7.5 event occurred 166 km east-southeast of Tadine. Most recently, a magnitude 7.0 earthquake took place on 31 March 2022 roughly 80 km from the 2004 epicenter. These events share similar epicentral regions and shallow focal depths, consistent with thrust faulting on or near the plate interface. The pattern indicates that the Loyalty Islands segment of the subduction zone releases strain through occasional great earthquakes separated by periods of relative quiescence. Ongoing monitoring by regional seismic networks remains essential for understanding recurrence intervals and potential tsunami hazards.

References

USGS Earthquake Catalog (events 2003–2022) Pacific Island Tectonics Overview, Geological Survey of New Caledonia