[6] Shore based observations had characterised the islands of the volcanic arc as having typical lavas and being of early Miocene or younger in age.

[3] However at the d'Entrecasteaux Ridge and Espiritu Santo central section there is localized compression of 50 mm (2.0 in)/year in the volcanic back arc to compensate.

[3] There has been asymmetric back-arc opening beyond the subduction zone in the North Fiji Basin and over the last 6 million years the Vanuatu chain has rotated about 28° clockwise.

[14][15] To the south subduction ceases at the triple junction with the Conway Reef microplate under the North Fiji Basin with the rest of the convergence being accommodated by less tectonically active rifting in the western stretch of the New Hebrides Trench, the Hunter Ridge to its north and the Hunter fracture zone which is a transform faulting fracture zone continuation of the trench towards Fiji.

[16] This triple junction is where from 3 million years ago the southernmost Central Spreading Ridge of the North Fiji Basin propagated southward and has now intersected with the New Hebrides Trench and the Hunter fracture zone.

[16] The progressive subduction/collision of the NW–SE trending Loyalty Ridge located on the Australian plate under the southern Vanuatu microplates produces much earthquake activity[3] but the most southernmost part of the trench south of latitude 22.5° S and east of longitude 170° E is not highly tectonically active[2] and translates into the non subducting Hunter fracture zone which is a transform faulting fracture zone.

[13] There are however other tectonic earthquakes associated with local plate boundaries nearby, as the North Fiji Basin has both spreading centres and fault zones and the most active parts are shown on a map on this page.

[19] It was modelled as a megathrust event having produced over 3 m (9.8 ft) of seafloor displacement but its position allowed attenuation by the Gilbert Islands of the wave that reached Hawaii.

[19] However modelling of the smaller tsunami that resulted from the Mw 7.7 2021 Loyalty Islands earthquake showed that other sea floor features could channel the tsunami from a larger Mw 8.2 earthquake at the same location north south, resulting in potential waves 1.5 m (4 ft 11 in) high at Norfolk Island and 1 m (3 ft 3 in)high on the West Coast of New Zealand.