M 7.6 - 82 km WNW of Hihifo, Tonga

Tectonic Summary

The May 10, 2023, M 7.6 Tonga earthquake occurred as the result of normal faulting at deep depths near the Tonga-Kermadec subduction zone. Focal mechanism solutions for the event indicate rupture occurred on either a moderately-dipping fault striking to the northeast, or a moderately-dipping fault striking southwest. From the location of the event, we infer that the event likely occurred within the subducted Pacific plate. At the location of the earthquake, the Pacific Plate and Australia Plate are converging at a velocity of 73 mm/yr.

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 May 10, 2023, earthquake are typically 75 km by 30 km (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.

The May 10, 2023, earthquake occurred in a seismically active region where five other earthquakes larger than magnitude 7 have occurred within 250 km in the previous 50 years. The largest event in the region was the 2009 M 8.1 earthquake, which occurred about 270 km to the east.

More information about the tectonics of the Tonga-Kermadec subduction zone is available on this story map.