Seismic Swarm PS20120202.1: February 2012 Activity West of Port-Vila, Vanuatu

A seismic swarm designated PS20120202.1 occurred 125 km west of Port-Vila, Vanuatu, beginning at 13:34 on 2 February 2012 and concluding at 06:01 on 3 February 2012. Over 16 hours and 26 minutes, the sequence produced 21 earthquakes. The initial event reached magnitude 7.1 at a depth of 23 km. Subsequent shocks included multiple magnitude 5.0–5.5 events clustered at shallow depths around 10 km, with later activity featuring a magnitude 6.1 event at 8 km depth on 3 February.

The swarm exhibited typical characteristics of clustered seismicity, with events distributed across depths from 3 km to 25 km. Magnitudes remained predominantly in the 5.0–5.5 range after the mainshock, indicating a rapid decay in energy release following the initial rupture.

Vanuatu occupies a tectonically active segment of the Pacific Ring of Fire, where the Indo-Australian Plate subducts beneath the Pacific Plate along the New Hebrides Trench. This convergence drives frequent earthquakes and volcanic activity throughout the archipelago. The region experiences high seismic strain accumulation, resulting in both isolated large events and episodic swarms.

Since 2000, eleven swarms have been recorded in the area, occurring in 2002 (two events), 2004 (one), 2005 (one), 2009 (three), 2010 (one), and 2011 (three). These episodes reflect the ongoing subduction dynamics and stress interactions along the plate boundary.

Notable strong earthquakes since 2000 include a magnitude 7.3 event on 17 December 2024 located 94 km from the swarm center, the 2012 magnitude 7.1 mainshock itself (46 km from center), two magnitude 7.3 shocks in August 2010 (82–89 km distant), and a magnitude 7.2 event in January 2002 (68 km from center). Such occurrences underscore the persistent seismic hazard in central Vanuatu.

The 2012 swarm contributed to the documented pattern of moderate-to-large events near the subduction interface, consistent with the area's long-term tectonic regime.

References
SeismoSight internal swarm classification records
USGS Earthquake Catalog (updated December 2024)