The 2021 M7.3 Deep Earthquake in the Vanuatu Region

On October 2, 2021, at 06:29 local time, a magnitude 7.3 earthquake occurred in the Vanuatu region at a focal depth of 527.0 km. This deep-focus event underscores the persistent tectonic forces operating along the western Pacific margin. Vanuatu occupies a tectonically active segment of the Pacific Ring of Fire. The islands form part of an island arc created by the northeastward subduction of the Indo-Australian plate beneath the Pacific plate along the New Hebrides Trench. Convergence rates in this zone average 7–10 cm per year, generating both shallow crustal earthquakes and deeper events within the descending slab. At depths exceeding 500 km, such earthquakes typically result from phase transitions or dehydration embrittlement in the cold subducting lithosphere rather than brittle failure near the surface. The 2021 event was the sole M7.3 earthquake recorded in the Vanuatu region since January 2000. Its great depth limited surface shaking and tsunami potential, consistent with the behavior of other intermediate- to deep-focus earthquakes worldwide. The broader geological history of Vanuatu reflects continuous arc volcanism and rapid uplift, producing the archipelago’s steep volcanic edifices and fringing coral reefs. Ongoing subduction sustains both seismic and volcanic hazards across the islands.

References

United States Geological Survey Earthquake Catalog Global Seismographic Network records