M 7.0 - 209 km SSE of Isangel, Vanuatu

Tectonic Summary

The September 14, 2022, M 7.0 Loyalty Islands earthquake occurred as the result oblique normal faulting, approximately 145 km beneath the Earth’s surface, on either a steeply or moderately dipping fault. Normal faulting at these depths is commonly interpreted as rupture within a subducting plate. At the location of this earthquake, the Australia plate moves roughly north relative to the Pacific at a velocity of 73 mm/yr, subducting beneath the Vanuatu island chain at the New Hebrides Trench. The September 14th event occurred near the boundary between these two plates and is likely a result of faulting within the subducting Australia slab, driven by the stresses generated by the bending of the plate as it sinks deeper into the mantle.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Earthquakes of this size are typically about 40x20 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 similar-magnitude shallow-focus earthquakes, but large intermediate-depth earthquakes may be felt at great distance from their epicenters.

The Loyalty Islands region is very active seismically, and the region within 250 km of the September 14, 2022, earthquake has hosted 27 other M 7+ earthquakes over the preceding century. The largest prior event within 250 km was a M7.6 on March 16, 1928. Because of their remote locations, earthquakes in this region as less likely to create strong shaking in populated areas.