Seismic Swarm Activity in the Vanuatu Region: December 2010

Vanuatu lies along the tectonically active boundary where the Australian Plate subducts beneath the Pacific Plate at rates exceeding 10 cm per year. This convergent margin produces frequent earthquakes, volcanic activity, and occasional seismic swarms throughout the archipelago. The region experiences elevated seismicity due to its position on the Pacific Ring of Fire, with most events occurring at shallow to intermediate depths along the subduction interface and within the overriding plate.

A seismic swarm designated PS20101231.1 was recorded in the Vanuatu region between 09:11 on 30 December 2010 and 04:11 on 31 December 2010. Over this 18-hour, 59-minute period, five earthquakes were registered. The sequence included events of magnitudes 5.0 to 5.1 at depths ranging from 10 km to 60 km. Specific timings and parameters were as follows: a magnitude 5.0 event at 09:11:50 on 30 December at 10 km depth; a magnitude 5.1 event at 09:11:56 on the same day at 48 km depth; a magnitude 5.0 event at 21:22:30 on 30 December at 20 km depth; a magnitude 5.1 event at 04:11:03 on 31 December at 10 km depth; and a magnitude 4.9 event at 04:11:10 on 31 December at 60 km depth.

This swarm occurred five days after a magnitude 7.3 earthquake located 141 km west of Isangel, Vanuatu, and approximately 43 km from the swarm center. Such clustering of moderate events following a larger mainshock is consistent with aftershock patterns or triggered activity along nearby fault segments in the subduction zone.

Historical records since 1 January 2000 indicate ten seismic swarms in the Vanuatu region. These occurred in 2002 (one swarm), 2004 (one), 2005 (one), 2006 (one), 2007 (one), 2008 (three), 2009 (one), and 2010 (one). The 2010 swarm represents the most recent in this series, underscoring the recurrent nature of swarm-type seismicity in this subduction setting.

Seismic swarms in Vanuatu often reflect fluid migration, stress transfer, or aseismic slip along the plate interface. The December 2010 sequence, with its shallow-to-intermediate depths and moderate magnitudes, aligns with typical activity along the New Hebrides trench segment. Ongoing monitoring by regional and global networks continues to track such patterns to improve understanding of subduction dynamics.

References
SeismoSight internal classification data for swarm PS20101231.1 and historical statistics.
USGS Earthquake Catalog for regional tectonic context and event parameters.