March 24, 2026 Earthquake: Tonga Islands

Tectonic Summary

The March 23, 2026, M 7.5 Tonga earthquake occurred as the result of normal faulting at intermediate depth. Focal mechanism solutions indicate rupture occurred on either a shallowly dipping fault striking southwest, or a steeply dipping fault striking northeast. In this region, the Pacific Plate subducts westward beneath the Australia Plate. The location and depth of the earthquake are consistent with faulting within the subducting Pacific Plate.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Normal faulting events of the size of the March 23, 2026, earthquake are typically about 70 km x 30 km in size (length x width).

Earthquakes like this event, with focal depths between 70 and 300 km, are commonly termed “intermediate-depth” earthquakes. Intermediate-depth earthquakes represent deformation within subducted slabs rather than at the shallow plate interface between subducting and overriding tectonic plates. They typically cause less damage on the ground surface above their foci than is the case with similar-magnitude shallow-focus earthquakes, but large intermediate-depth earthquakes may be felt at great distance from their epicenters.

Since 1950, six previous earthquakes of magnitude 7 or larger have occurred within 250 km of this earthquake. The most recent was a magnitude 7 in March 2025. The largest of these was a magnitude 8 earthquake on May 3, 2006, that caused minor damage in the region.

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