Seismic Swarm PS20241217.1 Near Port-Vila, Vanuatu

A seismic swarm designated PS20241217.1 occurred 64 km west-southwest of Port-Vila, Vanuatu, between 01:47 and 18:17 UTC on 17 December 2024. Over 16 hours and 29 minutes, the sequence included eight earthquakes with magnitudes ranging from 4.7 to 7.3 and focal depths between 30 and 54 km.

The largest event, magnitude 7.3 at 01:47:25 UTC and 54 km depth, initiated the swarm. Subsequent events included a magnitude 5.3 at 01:53:13 UTC (49 km depth), followed by smaller shocks of 4.7, 5.0, 5.0, 5.4, 5.2, and a final 5.5 at 18:17:23 UTC (46 km depth). Depths remained consistent within the upper to mid-crustal range typical of the regional subduction interface.

Vanuatu occupies a tectonically active segment of the Pacific Ring of Fire, where the Indo-Australian Plate subducts eastward beneath the Pacific Plate at rates exceeding 10 cm per year. This convergence produces frequent moderate-to-large earthquakes along the New Hebrides Trench. The December 2024 swarm epicenters align closely with this subduction zone, approximately 20–30 km from several prior magnitude 7+ events since 2000.

Historical records since 2000 document 20 swarms in the region, with notable clusters in 2011 (five events) and 2009 (three events). Strong earthquakes in the vicinity include the 7.3 event of 10 August 2010 located 22–23 km from the swarm center, two magnitude 7.1–7.2 shocks on 20 August 2011 (63–68 km distant), and a magnitude 7.2 event on 2 January 2002 (30 km away). The 17 December 2024 magnitude 7.3 mainshock occurred only 6 km from the swarm centroid, underscoring the persistent seismic hazard along this segment of the plate boundary.

Such swarms typically reflect stress adjustments along the megathrust or associated crustal faults rather than precursory activity for a single larger rupture. Depths of 30–54 km correspond to the seismogenic portion of the subduction interface, where brittle failure produces the observed sequences.

• SeismoSight internal swarm catalog PS20241217.1
• Historical earthquake database (2000–2024)