Seismic Swarm Near Sola, Vanuatu: The July 2010 Event in Regional Context

On 2 July 2010, a seismic swarm designated PS20100702.1 was recorded approximately 106 km west of Sola, Vanuatu. The sequence began at 06:04 UTC and concluded at 22:48 UTC, encompassing five earthquakes over 16 hours and 44 minutes. The events ranged in magnitude from 4.8 to 6.3, with focal depths between 29 km and 81 km. The largest shock, magnitude 6.3 at 29 km depth, initiated the swarm, followed by events of 5.3, 5.5, 5.0, and 4.8, most occurring at 35 km depth except one deeper shock at 81 km.

Vanuatu lies along the New Hebrides subduction zone, where the Australian plate descends beneath the Pacific plate. This tectonic setting produces frequent seismicity, with the northern Banks Islands region, including areas west of Sola on Vanua Lava, experiencing recurrent activity due to slab bending and dehydration processes at intermediate depths. The July 2010 swarm occurred within this active margin, consistent with patterns of clustered events driven by stress transfer along the plate interface.

Historical records since 2000 indicate six swarms in the vicinity, occurring in 2000 (one swarm), 2006 (one swarm), 2009 (three swarms), and 2010 (this event). Such swarms typically reflect transient stress adjustments rather than mainshock-aftershock sequences. The 2010 swarm followed two major earthquakes in 2009—a magnitude 7.7 event 148 km northwest of Sola and a magnitude 7.4 event 143 km northwest—along with a magnitude 7.2 shock on 27 May 2010 located 100 km west-northwest of Sola and only 14 km from the swarm centroid. These larger events likely influenced local stress fields, contributing to subsequent clustered activity.

The region’s seismicity forms part of the circum-Pacific belt, with Vanuatu averaging multiple magnitude 7+ earthquakes per decade. Depths in the 30–80 km range, as observed in the swarm, align with intermediate-depth seismicity linked to the subducting slab. No surface rupture or significant tsunami accompanied the 2010 sequence, typical for events of this scale offshore.

Ongoing monitoring highlights the persistent hazard in northern Vanuatu, where swarm activity serves as an indicator of evolving tectonic stress without necessarily preceding larger ruptures. The 2010 sequence underscores the dynamic nature of the subduction interface west of the Banks Islands.