Seismic Swarm PS20240911.1 Near Luganville, Vanuatu

A seismic swarm designated PS20240911.1 was recorded on 11 September 2024, approximately 123 km east-northeast of Luganville, Vanuatu. The sequence began at 18:17 UTC and concluded at 19:52 UTC, lasting 1 hour and 34 minutes. Five earthquakes were detected during this period, with magnitudes ranging from 4.8 to 5.8 and focal depths between 10 km and 18 km.

The individual events occurred at the following times and parameters: a magnitude 5.7 earthquake at 18:17:57 (depth 12 km), followed by a magnitude 5.1 event at 18:46:56 (depth 10 km). A magnitude 5.8 quake struck at 19:22:55 (depth 18 km), succeeded by a magnitude 4.8 event at 19:26:11 (depth 10 km) and a magnitude 5.0 earthquake at 19:52:23 (depth 16 km). These closely spaced occurrences within a compact timeframe characterize the swarm as a cluster of moderate seismic activity without a single dominant mainshock.

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 convergent boundary generates frequent earthquakes and volcanic activity across the archipelago. The region near Luganville, on the island of Espiritu Santo, lies directly above this subduction interface, resulting in persistent seismicity at shallow to intermediate depths. Historical records indicate that such swarms represent episodic releases of strain along fault systems within the overriding plate and along the plate interface.

Since 2000, ten seismic swarms have been documented in the vicinity, occurring in 2000, 2008, 2015, 2016 (two events), 2018, 2023 (three events), and 2024. These clusters highlight recurrent patterns of distributed seismicity rather than isolated large events. In addition, two strong earthquakes exceeding magnitude 7 have taken place within roughly 67 km of the current swarm center: a magnitude 7.3 event on 30 March 2016 and a magnitude 7.2 event on 1 August 2007. Both underscore the potential for significant energy release in this segment of the subduction zone.

The September 2024 swarm aligns with established regional behavior, where moderate events often occur in temporal groups without immediate escalation to larger ruptures. Continued monitoring remains essential given Vanuatu’s location on a highly active plate boundary.

References

SeismoSight internal swarm classification PS20240911.1
USGS Earthquake Catalog (historical events since 2000)
Global CMT Project (tectonic setting of Vanuatu subduction zone)