Shallow M6.2 earthquake hits Kermadec Islands region — third M6+ earthquake in 8 hours

The epicenter was located about 788 km (490 miles) SSW of ‘Ohonua, Tonga, and 1 032 km (703 miles) NE of Whangarei, New Zealand.

The USGS issued a Green alert for shaking-related fatalities and economic losses. There is a low likelihood of casualties and damage.

There is no tsunami threat from this earthquake.

Overall, the population in this region resides in structures that are highly resistant to earthquake shaking, though some vulnerable structures exist. The predominant vulnerable building types are reinforced masonry and unreinforced brick with timber floor construction.

This was the third M6+ earthquake in this region in just 8 hours on May 31, after M6.1 at 14:28 UTC and M6.0 at 21:21 UTC. Other earthquakes in this sequence include M4.8 at 16:14 UTC, M4.6 at 17:26 UTC, and another M4.8 at 20:16 UTC, all at a depth of 10 km (6.2 miles).

North of New Zealand, the Australia–Pacific boundary stretches east of Tonga and Fiji to a point 250 km (155 miles) south of Samoa. For 2 200 km (1 370 miles), the trench is approximately linear and includes two segments where old (over 120 million years) Pacific oceanic lithosphere rapidly subducts westward—Kermadec and Tonga.

At the northern end of the Tonga trench, the boundary curves sharply westward and transitions along a 700 km (435 miles) segment from trench-normal subduction, to oblique subduction, and finally to a left-lateral transform-like structure.

Australia–Pacific convergence rates increase northward from 60 mm per year (2.4 inches per year) at the southern Kermadec trench to 90 mm/yr (3.5 in/yr) at the northern Tonga trench; however, significant back arc extension, or equivalently, slab rollback, causes the consumption rate of subducting Pacific lithosphere to be much faster.

The spreading rate in the Havre Trough, west of the Kermadec trench, increases northward from 8 to 20 mm/yr (0.3 to 0.8 in/yr). The southern tip of this spreading center is propagating into the North Island of New Zealand, rifting it apart.

In the southern Lau Basin, west of the Tonga trench, the spreading rate increases northward from 60 to 90 mm/yr (2.4 to 3.5 in/yr), and in the northern Lau Basin, multiple spreading centers result in an extension rate as high as 160 mm/yr (6.3 in/yr). The overall subduction velocity of the Pacific plate is the vector sum of Australia–Pacific velocity and back arc spreading velocity: thus, it increases northward along the Kermadec trench from 70 to 100 mm/yr (2.8 to 3.9 in/yr), and along the Tonga trench from 150 to 240 mm/yr (5.9 to 9.4 in/yr).

The Kermadec–Tonga subduction zone generates many large earthquakes on the interface between the descending Pacific and overriding Australia plates, within the two plates themselves, and, less frequently, near the outer rise of the Pacific plate east of the trench.

Since 1900, 40 M7.5+ earthquakes have been recorded, mostly north of 30°S. However, it is unclear whether any of the few historic M8+ events that have occurred close to the plate boundary were underthrusting events on the plate interface, or were intraplate earthquakes.

On September 29, 2009, one of the largest normal fault (outer rise) earthquakes ever recorded (M8.1) occurred south of Samoa, 40 km (25 miles) east of the Tonga trench. The earthquake generated a tsunami that killed at least 180 people. Maximum wave heights were measured at over 12 m (39 feet) in Samoa, more than 17 m (56 feet) in American Samoa, and up to 22 m (72 feet) in Tonga, resulting in widespread coastal devastation.

Estimated population exposure to earthquake shaking

Regional seismicity

References:

¹ M6.2 earthquake Kermadec Islands – USGS – May 31, 2025

² M6.2 earthquake Kermadec Islands – EMSC – May 31, 2025