Seismic Swarm PS20090602.1: Activity Near Port-Vila, Vanuatu

A seismic swarm designated PS20090602.1 occurred 66 km west of Port-Vila, Vanuatu, between 21:25 on 1 June 2009 and 16:01 on 2 June 2009. Over 18 hours and 36 minutes, the sequence produced seven earthquakes. The events ranged in magnitude from 5.0 to 6.3, with depths between 15 km and 60 km. The largest shock, magnitude 6.3 at 15 km depth, struck at 02:17 on 2 June, followed within minutes by two magnitude 5.7 and 5.5 events at similar shallow depths. Subsequent shocks included magnitudes 5.5, 5.0, 5.5, and a final 5.0 event that closed the swarm.

Vanuatu lies along the Pacific Ring of Fire at the convergent boundary where the Indo-Australian plate subducts beneath the Pacific plate. This tectonic setting generates frequent seismicity, volcanic activity, and occasional tsunamis. The island arc experiences both shallow crustal events and deeper events within the subducting slab, consistent with the depth range observed during the 2009 swarm.

Since 2000, four swarms have been recorded in the region, including the 2009 sequence. Earlier swarms occurred in 2002 (two events), 2004 (one event), and 2005 (one event). Stronger individual earthquakes have also struck nearby. Notable examples include a magnitude 7.3 event 24 km west-northwest of Port-Vila on 17 December 2024, a magnitude 7.3 shock 33 km northwest of Port-Vila on 10 August 2010, and additional magnitude 7.1–7.2 events in 2011, 2012, and 2002, all within tens of kilometres of the swarm centre.

The 2009 swarm illustrates the episodic clustered behaviour that characterises Vanuatu’s seismicity. While individual events remained moderate, their rapid succession within a compact area reflects the dynamic stress regime driven by ongoing plate convergence. Continued monitoring supports regional hazard assessment in this highly active tectonic environment.

References
USGS Earthquake Catalog
SeismoSight internal swarm classification PS20090602.1