Wallis and Futuna

Wallis and Futuna is a French territory comprising three volcanic islands in the southwest Pacific, situated between Fiji to the west and Samoa to the east, at a critical location where the seismically intense Tonga-Fiji plate boundary system exerts direct tectonic influence. The territory sits approximately 200 to 300 kilometres west of the Tonga Trench and north of the complex Fiji Platform, in a zone where the geometry of [[plate-tectonics]] becomes extremely complicated as the Tonga-Kermadec [[subduction]] system transitions to the broader Fiji-Vanuatu arc junction. The Pacific Plate is consumed along the Tonga Trench to the east at rates up to 240 millimetres per year — the fastest on Earth — and the seismic energy released by this [[subduction]] is strongly felt at Wallis and Futuna. Deep intraslab earthquakes within the subducted Pacific slab beneath and east of the territory, intermediate-depth events, and occasional shallow crustal events all contribute to the islands' seismic exposure. The volcanic islands themselves — Wallis ('Uvea) and the Futuna-Alofi pair — are geologically young arc volcanic edifices, indicating that the territory has recently been in or near the volcanic arc environment.

The seismic history of Wallis and Futuna is dominated by large events from the Tonga system. The 3 March 1954 earthquake ([[moment-magnitude]] 7.1) caused felt shaking. The 9 June 1994 Bolivia deep-focus earthquake ([[moment-magnitude]] 8.2 at 647 kilometres depth) was felt as far-field motion across the southwest Pacific including Wallis. The 2009 Samoa [[moment-magnitude]] 8.1 outer-rise earthquake generated a regional [[tsunami]] that reached Wallis and Futuna; wave heights were approximately 1 to 2 metres at the low-lying coastal areas of 'Uvea, causing some coastal inundation and disruption. The 2022 Hunga Tonga-Hunga Ha'apai volcanic eruption generated a [[tsunami]] that struck Wallis and Futuna within approximately 30 minutes of the eruption — among the shortest warning times of any affected territory — producing wave heights of 1 to 3 metres and causing coastal flooding and damage at 'Uvea. The proximity of the Tonga arc and trench to the territory means that future large Tonga megathrust events pose a significant [[tsunami]] risk with very limited warning time.

The tectonic and geological evolution of Wallis and Futuna reflects the arc volcanic history of the southwest Pacific. The volcanic islands are composed of basaltic and andesitic lavas erupted from the arc volcanic system above the subducting Pacific slab; the chemistry of Futuna's lavas in particular shows a signature consistent with arc volcanism above an active [[subduction]] zone. The complex back-arc and inter-arc geometry of the Fiji-Tonga system means that the tectonic environment is more diffuse and multi-directional than a simple single-arc setting. The Lau Basin back-arc spreading centre to the south represents active extensional tectonics driven by Tonga slab rollback, and its seismicity occasionally produces felt events at Wallis and Futuna. [[liquefaction]] is a potential concern for the low-lying coastal deposits of 'Uvea during moderate-to-large shallow earthquakes, given the presence of young beach and lagoonal sediments. France's Bureau de Recherches Géologiques et Minières (BRGM) contributes to seismological monitoring of the territory through the regional network.