[S-TT40] Synthetic Aperture Radar and its application

[STT40-06] Detection of the 2023 Royalty Island earthquake tsunami by SWOT satellite

*Kiyohiro Ishijima^1,2, Shingo Watada³ (1.Department of Earth Planetary Science, School of Science, The University of Tokyo, 2.MRI Research Associates Inc., 3.Earthquake Research Institute, The University of Tokyo)

Keywords:Tsunami Observation, InSAR, NASA SWOT, Surface Water and Ocean Topography

Interferometric SAR has been widely used to observe ground surface deformation, however, there have been few attempts to use InSAR to observe tsunamis because not only the back scattered phases are not maintained due to the incessantly changing sea surface conditions but also the difficulty in removing the effects of temporal and spatial change of the sea level due to various factors. On the other hand, SWOT (Surface Water and Ocean Topography), an interferometric SAR satellite operated by NASA to observe the water level change on land and sea can measure the water surface height in a single pass by emitting microwaves at the same time from two antennas on the left and right in the radial direction of the satellite track. High-precision observations of water level fluctuations are used to monitor water level changes in lakes and swamps on land and to forecast river flooding. In this study, we present an attempt to observe a tsunami in an open ocean using NASA SWOT, using the tsunami caused by the M7.7 earthquake that occurred near the Loyalty Islands in May 2023 as an example (Faugère et al., 2024). On May 19, 2023 at about 02:57 UTC, an M7.7 earthquake occurred near the Loyalty Islands, and a 0.61m tsunami was observed in Lenakel, Vanuatu, a town near the epicenter. The NASA SWOT passed over the area about 900 km above the epicenter at 25°S and 175° E about one hour after the earthquake and observed the sea surface height. We used the sea level data from the NASA SWOT observations, corrected for tidal variations, to confirm the propagation of the sea surface variations in the direction away from the epicenter. The spatial pattern of the sea surface fluctuations was somewhat consistent with the results of the tsunami numerical simulation based on a finite fault model (Fujii, 2023), indicating that the tsunami had been detected by SWOT.