Seismic Swarm PS20110204.1: Analysis of Activity Near Sola, Vanuatu

A seismic swarm designated PS20110204.1 occurred in the waters west-southwest of Sola, Vanuatu, beginning at 14:20 on 4 February 2011 and concluding at 08:37 on 5 February 2011. Over 18 hours and 16 minutes, the swarm produced six earthquakes with magnitudes ranging from 5.0 to 5.9. Event times, magnitudes, and depths were recorded as follows: a 5.9 magnitude quake at 10 km depth at 14:20:55 on 4 February; a 5.8 magnitude event at 48 km at 14:21:01; a 5.4 magnitude shock at 10 km at 15:23:10; a 5.1 magnitude quake at 60 km at 15:23:20; a 5.2 magnitude event at 10 km at 16:21:10; and a final 5.0 magnitude quake at 42 km at 08:37:22 on 5 February.

Vanuatu occupies a tectonically active segment of the Pacific Ring of Fire, where the Indo-Australian Plate subducts beneath the Pacific Plate along the Vanuatu Trench. This convergent boundary drives frequent seismicity, with the central and northern islands, including the Banks Islands near Sola, experiencing elevated activity due to oblique subduction and associated faulting. Depths in the recorded swarm, spanning 10 km to 60 km, align with typical patterns of intermediate-depth events in this subduction zone.

Since 2000, eight swarms have been documented in the region, occurring in 2000 (one swarm), 2006 (one), 2008 (one), 2009 (three), and 2010 (two). These clusters reflect episodic stress release along the plate interface without a dominant mainshock. The 2011 swarm fits this pattern, with closely spaced events indicating localized crustal adjustment.

Notable strong earthquakes since 2000 include a magnitude 7.2 event on 27 May 2010 located 100 km west-northwest of Sola (59 km from the swarm center) and a magnitude 7.0 quake on 8 January 2023 situated 23 km west-northwest of Port-Olry (91 km from the swarm center). Both underscore the persistent seismic hazard in the broader area.

This swarm provides insight into the region's ongoing tectonic dynamics, highlighting how clustered moderate-magnitude events can signal accumulating strain in the subduction zone. Such activity contributes to the long-term seismic record used for hazard assessment in Vanuatu.

References: SeismoSight internal classification data for swarm PS20110204.1 and historical statistics. USGS earthquake catalog for regional strong events since 2000.