Deep M7.0 Earthquake South of the Fiji Islands

A magnitude 7.0 earthquake struck south of the Fiji Islands on November 9, 2022, at 09:51 UTC. The event originated at a depth of 660 km, placing it within the lower mantle transition zone. This deep-focus quake occurred in a region characterized by intense tectonic activity driven by subduction processes. The Fiji Islands lie at the boundary between the Pacific and Australian plates. Here, the Pacific plate subducts westward beneath the Australian plate along the Tonga Trench, generating one of the most seismically active zones on Earth. Subduction produces both shallow and deep earthquakes, with the latter resulting from phase changes in mantle minerals at depths exceeding 400 km. At approximately 660 km, the transition from ringwoodite to perovskite and magnesiowüstite can trigger brittle failure, allowing seismic energy to propagate through otherwise ductile material. This M7.0 event represents the sole strong earthquake recorded in the immediate area since January 1, 2000. Its great depth limited surface effects, with no significant damage or tsunami reported despite the high magnitude. Deep events in this setting often exhibit complex rupture patterns influenced by the cold, rigid slab material descending into the mantle. Historically, the southwest Pacific subduction system has produced numerous deep-focus earthquakes, contributing to our understanding of mantle dynamics. The 660 km discontinuity acts as a barrier that can both impede and localize slab deformation, occasionally releasing stored strain in large events. Continued monitoring of such quakes provides data on slab temperature, mineralogy, and the mechanics of deep seismicity. Seismic networks operated by international agencies recorded the 2022 event clearly, confirming its parameters and aiding studies of mantle structure beneath Fiji. Future research may refine models of how subducting slabs interact with the 660 km boundary, improving global assessments of deep earthquake hazards.

References

USGS Earthquake Catalog Incorporated Research Institutions for Seismology (IRIS) Event Search