Location:

Period:

19 Aug 2018 01:01:11 - 20 Aug 2018 20:09:58 (1 day 19 hours 8 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

2 swarms found nearby.

2018

PS20180819.1(25.5km)

19 Aug

2 days 6 hours

22 earthquakes

S20180819.3(25.0km)

19 Aug

3 days 0 hours

40 earthquakes

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Seismic Swarm S20180819.2: Deep-Focus Activity East of Fiji

Seismic swarm S20180819.2 occurred approximately 294 km east of Levuka, Fiji, between 01:01 on 19 August 2018 and 20:09 on 20 August 2018. During this 43-hour period, 36 earthquakes were recorded, with magnitudes ranging from 4.1 to 4.9 and focal depths between 523 km and 625 km. All events clustered tightly in both space and time, characteristic of swarm behavior without a distinct mainshock-aftershock sequence.

The swarm's depth distribution places the activity within the lower mantle transition zone of the subducting Pacific slab. Such deep-focus seismicity arises from transformational faulting or dehydration embrittlement as the slab descends through phase transitions near 520–660 km. The recorded events showed no significant temporal migration in depth or magnitude, indicating a localized stress release within a confined volume of the slab.

Fiji lies at the northeastern edge of the Australian Plate, where complex interactions among the Pacific, Australian, and several microplates produce one of the world's most active deep-earthquake zones. The region has experienced deep seismicity exceeding 600 km depth since instrumental recording began. Historical data indicate that only two swarms have been identified in this sector since 1 January 2000, with S20180819.2 representing the first such episode.

The 2018 swarm events maintained remarkably consistent focal depths around 560–610 km, suggesting rupture within a narrow, high-pressure layer of the slab. Magnitudes remained moderate (maximum 4.9), consistent with the limited rupture dimensions possible at these depths due to increased confining pressure and elevated temperatures.

Continued monitoring of the Fiji deep seismic zone remains essential for understanding slab dynamics and potential precursory patterns. The 2018 swarm provides a valuable dataset for refining models of deep earthquake nucleation in the western Pacific.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
Pacific Ring of Fire tectonic summaries, USGS Professional Papers