Seismic Swarm PS20100527.1: Analysis of Activity Near Sola, Vanuatu

A seismic swarm designated PS20100527.1 occurred approximately 79 km west of Sola, Vanuatu, from 17:14 on 27 May 2010 to 14:57 on 28 May 2010. Over 21 hours and 43 minutes, nine earthquakes were recorded in this sequence. The events began with a magnitude 7.2 mainshock at a depth of 31 km, followed by eight aftershocks ranging from magnitude 4.6 to 6.1, predominantly at depths of 34–35 km.

The temporal distribution shows the largest event initiating the swarm, with subsequent activity clustered within the first few hours and tapering over the following day. This pattern reflects typical aftershock decay following a significant rupture in a subduction-related setting. Magnitudes included one event at 6.1 and several between 5.0 and 5.8, indicating moderate energy release beyond the mainshock.

Vanuatu occupies a tectonically active segment of the Pacific Ring of Fire along the New Hebrides subduction zone. Here, the Indo-Australian Plate subducts eastward beneath the Pacific Plate at rates exceeding 10 cm per year, generating frequent intermediate-depth earthquakes. The region’s geology features volcanic island arcs, including the islands around Sola on Vanua Lava, formed by this ongoing convergence. Historical records document persistent seismicity, with the swarm location lying near the western margin of the Vanuatu archipelago where slab-related stresses concentrate.

Since 1 January 2000, six swarms have been identified in the area, occurring in 2000 (1 swarm), 2006 (1), 2008 (1), and 2009 (3). Strong earthquakes in the vicinity include the magnitude 7.2 event of 27 May 2010 itself, located 100 km west-northwest of Sola and 16 km from the swarm center. Additional notable events comprise a magnitude 7.4 quake on 7 October 2009 (143 km northwest of Sola) and a magnitude 7.7 event on the same date (148 km northwest of Sola), situated 79 km and 88 km from the swarm epicenter, respectively. These occurrences underscore the zone’s capacity for repeated large-magnitude ruptures.

The 2010 swarm fits within this framework of clustered activity driven by plate-boundary deformation. Depths around 35 km align with the upper portion of the subducting slab, where frictional locking and fluid migration can trigger sequences of events. Such swarms provide insight into stress transfer along the interface without necessarily indicating an imminent larger rupture.

References

USGS Earthquake Hazards Program catalog (historical events and parameters).
Global CMT Project focal mechanism database (tectonic context).
Geoscience Australia seismic reports (regional Vanuatu activity summaries).