Presentation Information
[P17-02]Inversion analysis of the 2023 Loyalty Island earthquake tsunami by SWOT satellite
*Kiyohiro Ishijima1,2, Shingo Watada3 (1. Department of Earth and Planetary Science, The University of Tokyo, 2. MRI Reseach Associates Inc., 3. Earthquake Research Institute, The University of Tokyo)
干渉SARはこれまで地表変動の観測によく用いられてきた．一方で，海表面変動の一つである津波に伴う海面の水位変化の干渉SARを用いた計測は，海面状態が時事刻々変化し前後する時刻の後方散乱位相が保持されないことや，様々な要因で生じる時間空間変動する海面高の影響を除去することが困難なため，これまでなされてこなかった．一方，NASAが運用している陸域および海域の水面変動観測を目的とした干渉SAR，SWOT (Surface Water and Ocean Topography、2022年12月より観測開始)は，衛星進行方向に対して左右にある2つのアンテナから同時にマイクロ波を照射し，一つの衛星軌道で水面からの後方散乱したSAR画像を干渉させ，水面高度計測を可能としている．陸域の高精度水面変動観測結果は，湖沼の水位変化監視や河川の氾濫予測などに用いられている．本研究では，2023年5月19日02:57(UTC)頃にローヤリティー諸島付近で発生したM7.7の地震による津波を対象に，NASA SWOTの観測データのうち潮位変動の補正を行った海面高データを用いて，震源域から遠ざかる方向に伝播している水面変動とフォワードシミュレーションを比較することで津波シグナルである水位変動を検出していることを確認した，また，NASA SWOTの水面変動観測結果を用いた津波インバージョン解析の試みについて報告する．
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, launched in December 2022), 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 separated in the ground range direction. 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 analyse the tsunami generated by the M7.7 earthquake near the Loyalty Islands on May 19, 2023, using observation data from NASA’s SWOT mission through an inversion approach.
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, launched in December 2022), 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 separated in the ground range direction. 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 analyse the tsunami generated by the M7.7 earthquake near the Loyalty Islands on May 19, 2023, using observation data from NASA’s SWOT mission through an inversion approach.