Potential tsunami hazard of the southern Vanuatu subduction zone: Tectonics, case study of the Matthew Island tsunami of 10 February 2021 and implication in regional hazard assessment

Abstract

The Vanuatu subduction zone (VSZ) is known to be seismically very active, due to the high convergence rate between the Australian and Pacific tectonic plates for the majority of the margin. However, this is not the case on its southernmost part south of latitude 22.5g€¯S and east of longitude 170g€¯E, which is neither highly tectonically active nor has it produced large tsunamis over the past 150 years. It has also not been widely studied. On the 11 February 2021 (10 February UTC), a magnitude Mw 7.7 earthquake triggered a tsunami warning in New Caledonia and Vanuatu 20g€¯min after midnight (local time). With an epicentre located close to the volcanic islands of Matthew and Hunter, this shallow reverse-faulting rupture ( g€¯28g€¯cm wave amplitudes were recorded at eight different coastal gauges, including one with an amplitude of more than 1g€¯m (Lenakel, Tanna, Vanuatu). The tsunami threat at that location would be large enough to warrant an onshore evacuation. Finally, it helps to highlight the significant role played by the numerous submarine features in the region, the Norfolk Ridge being the most important, which acts like a waveguide from the north to the south.