M 7.3; Vanuatu; (10 Aug 2010) (49km from the swarm center)
M 7.3; 33 km NW of Port-Vila, Vanuatu; (10 Aug 2010) (48km from the swarm center)
M 7.2; 50 km WNW of Port-Vila, Vanuatu; (2 Jan 2002) (50km from the swarm center)
Seismic Swarm PS20200527.1: Analysis of Activity Near Port-Vila, Vanuatu
A seismic swarm designated PS20200527.1 occurred approximately 78 km north-northwest of Port-Vila, Vanuatu, between 22:52 on 26 May 2020 and 08:08 on 27 May 2020. Over 9 hours and 15 minutes, five earthquakes were recorded, with magnitudes ranging from 4.5 to 6.2 and focal depths between 9 and 10 km. The sequence began with a magnitude 5.5 event at 22:52 on 26 May, followed by two closely spaced events of magnitudes 6.2 and 6.1 at 07:09 on 27 May. Additional events included a magnitude 5.0 quake at 08:05 and a magnitude 4.5 event at 08:08, both on 27 May. All events clustered at shallow depths, consistent with typical swarm behavior in the region.
Vanuatu occupies a tectonically active position within the Pacific Ring of Fire, where the Pacific Plate subducts beneath the Australian Plate along the New Hebrides Trench. This convergent boundary drives frequent seismicity, including both isolated large earthquakes and episodic swarms. The area around Port-Vila experiences elevated activity due to its proximity to the subduction interface and associated fault systems. Shallow depths of 9–10 km for the 2020 swarm align with crustal deformation above the megathrust zone.
Historical records since 2000 indicate 15 prior swarms in the vicinity, occurring in 2002 (two events), 2004, 2005, 2009 (three events), 2010, 2011 (three events), 2012, 2015, 2016, and 2018. These swarms reflect episodic stress release along the subduction margin. Stronger independent earthquakes have also struck nearby, including a magnitude 7.3 event 24 km west-northwest of Port-Vila on 17 December 2024, located 64 km from the swarm center. Earlier magnitude 7.3 events occurred on 10 August 2010 at distances of 49 km and 48 km from the center, while a magnitude 7.2 quake took place 50 km west-northwest of Port-Vila on 2 January 2002. Such events underscore the persistent seismic hazard in central Vanuatu.
The 2020 swarm, characterized by rapid succession and moderate magnitudes without a dominant mainshock-aftershock pattern, provides insight into localized stress migration along shallow crustal faults. Continued monitoring remains essential given Vanuatu’s position on an active plate boundary.
References
- SeismoSight internal swarm classification database (PS20200527.1 parameters).
- USGS Earthquake Catalog (strong event locations and magnitudes since 2000).