Seismic Swarm PS20100810.1: Analysis of the August 2010 Event Near Port-Vila, Vanuatu

Vanuatu occupies a tectonically active segment of the Pacific Ring of Fire, where the Australian Plate subducts beneath the Pacific Plate along the New Hebrides Trench. This convergent margin produces frequent earthquakes, volcanic activity, and occasional seismic swarms driven by stress accumulation and fluid migration within the subduction zone. The region around Port-Vila, on the island of Efate, lies near the trench axis and experiences elevated seismicity at depths typically ranging from 25 to 160 km.

Seismic swarm PS20100810.1 was recorded 72 km west-northwest of Port-Vila. The sequence began at 05:23 on 10 August 2010 and concluded at 12:53 on 12 August 2010, spanning 55 hours and 30 minutes. During this interval, 23 earthquakes were detected. The swarm opened with two magnitude-7.3 events at 05:23:44 and 05:23:51, occurring at depths of 25 km and 80 km respectively. Subsequent activity consisted of moderate events between magnitude 5.0 and 5.9, clustered predominantly at depths of 27–42 km, with a few deeper outliers reaching 140–156 km.

The temporal distribution shows peak activity on 10 August, followed by a gradual decline through 11 and 12 August. Notable later events included a magnitude-5.9 earthquake at 03:35 on 11 August and magnitude-5.5 events on 11 and 12 August. Depths remained consistent with the shallow-to-intermediate interface of the subduction zone, consistent with the regional tectonic setting.

Since 1 January 2000, seven swarms have been documented in the broader area. Earlier episodes occurred in 2002 (two swarms), 2004 (one swarm), 2005 (one swarm), and 2009 (three swarms). The 2010 sequence aligns with this pattern of episodic clustering rather than isolated mainshock-aftershock sequences.

Strong earthquakes since 2000 include a magnitude-7.3 event 24 km west-northwest of Port-Vila on 17 December 2024, a magnitude-7.1 event 125 km west of Port-Vila on 2 February 2012, two magnitude-7.3 events on 10 August 2010 located 26 km and 32 km from the swarm center, and a magnitude-7.2 event 50 km west-northwest of Port-Vila on 2 January 2002. These events illustrate the persistent high-magnitude potential of the New Hebrides subduction interface.

Seismic swarms in this setting typically reflect transient stress changes along the plate boundary, often preceding or accompanying larger ruptures. The 2010 swarm's proximity to subsequent strong events underscores the value of continuous monitoring for understanding subduction-zone dynamics.

References
SeismoSight internal swarm classification records (PS20100810.1)
USGS earthquake catalog (events 2000–2024)