Seismic Swarm Activity East of Luganville, Vanuatu: July 2024 Event Analysis

A seismic swarm designated PS20240722.1 occurred approximately 94 km east of Luganville, Vanuatu, on 22 July 2024. The sequence began at 05:04 local time and concluded at 14:38, spanning 9 hours and 34 minutes. During this period, six earthquakes were recorded, with magnitudes ranging from 4.5 to 6.1 and focal depths between 4 km and 158 km.

The swarm initiated with two closely spaced events at 05:04, registering magnitudes of 5.2 and 6.1 at shallow depths of 10 km and 4 km, respectively. A third event of magnitude 6.1 occurred seconds later at a greater depth of 158 km. Subsequent activity included a magnitude 4.5 quake at 06:06, followed by a magnitude 5.0 event at 06:08, both at 10 km depth. The swarm concluded with another magnitude 5.0 earthquake at 14:38, also at 10 km depth. These events reflect typical clustered seismic behavior in an active tectonic setting, where multiple shocks occur without a single dominant mainshock.

Vanuatu lies within the Pacific Ring of Fire along the New Hebrides subduction zone, where the Pacific Plate subducts beneath the Australian Plate. This convergent boundary drives frequent seismic and volcanic activity across the archipelago. The region experiences elevated earthquake rates due to ongoing plate convergence at rates of approximately 5–10 cm per year, resulting in both shallow crustal events and deeper intraslab seismicity.

Historical records indicate nine prior swarms in the area since 2000, occurring in 2000, 2008, 2015, 2016, 2018, 2020, and three instances in 2023. Notable strong earthquakes since 2000 include a magnitude 7.2 event 56 km east of Luganville in August 2007, a magnitude 7.0 quake 3 km northwest of Norsup in April 2016, and a magnitude 7.3 event 48 km east-northeast of Luganville. These occurrences underscore the persistent seismic hazard in the vicinity of the July 2024 swarm.

Such swarms provide valuable data for monitoring tectonic stress accumulation and may precede or follow larger events, though most remain moderate in impact. Ongoing surveillance by regional seismic networks supports improved hazard assessment in this high-risk zone.

References:
USGS Earthquake Catalog
Global CMT Project
SeismoSight internal swarm classification data