First mapping of a tsunami wavefield by SWOT satellite: observation data and preliminary numerical simulation of the 19 May 2023 tsunami near the Loyalty Islands

Abstract. The NASA-CNES altimetry mission SWOT (Surface Water and Ocean Topography) deployed in December 2022 embarks a Ka-band Radar Interferometer (KaRIn), providing a 120 km-wide swath sea level measurement. On 19 May 2023, SWOT was able to record a 2D signature of the tsunami generated by the Mw 7.7 earthquake southeast of the Loyalty Islands (southwest Pacific Ocean), about 1 h after the earthquake, on a straight SSW-NNE path. Comparison between numerical models and real measurements was performed to assess SWOT's ability to monitor tsunami waves. A uniform coseismic slip rupture model allows to satisfactorily fit the regional observations. Testing models against a dynamic representation of the tsunami wavefield (instead of static) show a good phase agreement, but simulated amplitudes are lower than the measurements. However, this SWOT unprecedented 2D observation critically inform on tsunami propagation and modelling, and offer a breakthrough perspective for better predictions.