[H-DS06] 津波とその予測

[HDS06-06] Numerical simulation of tsunami and magnetic signals at Chichijima Island, Japan, after the eruption of Hunga volcano, Tonga, on January 15, 2022

*南 拓人¹、柴原 澪¹、浅利 晴紀³、藤 浩明² (1.神戸大学大学院理学研究科惑星学専攻新領域惑星学講座、2.京都大学大学院理学研究科附属地磁気世界資料解析センター、3.気象庁柿岡地磁気観測所)

キーワード：父島、火山、磁場、トンガ、数値シミュレーション

The Hunga Tonga volcano, Tonga (hereafter referred to as Hunga volcano) erupted around 4:15 on January 15, 2022, UTC. This eruption caused large tsunamis reaching the Japan coasts with the tsunami heights over 1.0 m. As in Chichijima, the tide gauge recorded ~0.8 m about 10 hours after the eruption. We identified tsunami-related magnetic signals observed at the magnetic station Chichijima (CBI), operated by Japan Meteorological Agency (JMA), which started around 13:30 on January 15 UTC and had almost the same periodicity of ~20 min as the tide record at the adjacent tide station Chichijima Futami that also started around 13:30 on Januray 15 UTC. To understand both tide record and magnetic data at Chichijima simultaneously, we so far performed two types of tsunami simulations; one is the normal tsunami simulation with the source at the eruption point and the other is the pressure wave driven tsunami simulation. In the pressure-driven tsunami simulation, we used the cocentric propagation of pressure wave from the eruption point with the velocity of 317 m/sec, referring to the result of Gusman et al. (2022). The adopted pressure waveform was the same as the pressure data observed at Chichijima Island. As a result, our simulation suceeded in reproducing the tide record at Chichijima except the time window from 9 to 10 hours after the eruption. Befor 9 hors, the tide record was explained by the pressure-driven tsunami simulation, while the data after 10 hours were done by the normal tsunami simulation. Almost the same periodicity of the magnetic data as the tide record data from 9 to 10 hours after the eruption indicates that there were definitely some significant tsunami velocity field surrounding Chichijima Island at the time window. In the presentation, we will report our numerical simulation and discuss possibel reasons for the observed tsunami and magnetic varation from 9 to 10 hours after the eruption at Chichijim Island.