Seismic Activity South of the Kermadec Islands: The 2020 Magnitude 7.4 Event

The Kermadec Islands form a volcanic arc northeast of New Zealand, situated above the Kermadec-Tonga subduction zone. Here the Pacific Plate converges with and subducts beneath the Australian Plate at rates exceeding 5 cm per year, generating one of Earth’s most active tectonic boundaries. This convergence produces frequent earthquakes, many at shallow depths, along with arc volcanism. On 18 June 2020 at 12:49 UTC, a magnitude 7.4 earthquake occurred south of the Kermadec Islands. The event originated at a depth of 10.0 km. According to available records, this earthquake represents the sole strong event (M ≥ 7.0) recorded in the immediate area since 1 January 2000. Shallow-focus earthquakes in subduction zones commonly result from thrust faulting on the plate interface or within the overriding plate. The 10 km depth placed the rupture in the brittle upper crust, where elastic strain can accumulate rapidly before release. Although the epicenter lay far from inhabited islands, such events illustrate the persistent seismic hazard along the trench. The broader Kermadec subduction system has shaped regional geology for millions of years. Continuous plate motion sustains both megathrust earthquakes and normal-faulting events within the bending Pacific Plate seaward of the trench. Volcanic edifices of the Kermadec arc, built from magma generated by slab dehydration, further attest to ongoing subduction. Monitoring by regional seismic networks continues to track activity along this margin, providing data essential for understanding rupture processes and tsunami potential in remote oceanic settings.

References

USGS Earthquake Catalog (event parameters for 18 June 2020).
Global CMT Project (tectonic setting of the Kermadec subduction zone).