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Location:
265 km E of Levuka, Fiji
Period:
19 Aug 2018 00:46:00 - 22 Aug 2018 00:46:51 (3 days)
Volcanoes in 100km radius:
None
Earthquakes:
40
2 swarms found nearby.
2018
PS20180819.1(23.0km)
19 Aug
2 days 6 hours
22 earthquakes
S20180819.2(25.0km)
19 Aug
1 day 19 hours
36 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20180819.3: Deep Earthquake Activity East of Levuka, Fiji

A notable seismic swarm, designated S20180819.3, occurred approximately 265 km east of Levuka, Fiji, between 19 and 22 August 2018. The sequence began at 00:46 UTC on 19 August and concluded at the same time on 22 August, spanning 72 hours and encompassing 40 earthquakes. All events registered magnitudes between 4.0 and 4.8 and originated at depths ranging from 483 km to 648 km, placing them well within the mantle.

Fiji lies at the complex junction of the Pacific and Australian plates, where the Pacific Plate subducts westward beneath the Australian Plate along the Tonga-Kermadec Trench system. This tectonic setting produces frequent deep-focus seismicity as the cold, brittle subducted slab descends into the mantle transition zone. The Fiji Plateau itself forms part of a broader extensional regime influenced by back-arc spreading and strike-slip faulting, contributing to the region's elevated seismic hazard.

The August 2018 swarm exhibited characteristics typical of deep intraslab activity, with events clustered in both time and space. Magnitudes remained moderate, and the temporal distribution showed a rapid onset followed by a gradual decline in frequency over the three-day period. Depths consistently exceeded 500 km for the majority of events, consistent with dehydration embrittlement or transformational faulting mechanisms proposed for deep earthquakes in subducted slabs.

Since 1 January 2000, only one swarm has been recorded in this specific offshore sector east of Levuka. The 2018 sequence therefore represents the sole documented swarm in the modern instrumental record for the area, underscoring the episodic nature of clustered deep seismicity in this portion of the Fiji region.

Such deep swarms provide valuable constraints on slab dynamics and stress transfer within the mantle. Continued monitoring by regional seismic networks enhances understanding of Fiji's long-term seismic behavior and supports improved hazard assessment for nearby island communities.

References

SeismoSight internal swarm classification S20180819.3
USGS Earthquake Catalog (global deep-event records)
Pacific Island regional tectonic summaries from Geoscience Australia