14:00 〜 14:15
[HDS10-07] Tsunami-related magnetic signals observed at Chichijima Island, Japan, after the eruption of Hunga volcano, Tonga, on January 15, 2022
キーワード：トンガ、磁場、津波、フンガ火山、噴火、父島
The Hunga Tonga volcano, Tonga (hereafter referred to as Hunga volcano) erupted around 4:00 on January 15, 2022, UTC. The Volcanic Explosivity Index (VEI) is estimated to be 5 to 6, which was judged from the altitude of 30 km the plume reached (GSJ reports: https://www.gsj.jp/en/hazards/volcano/tonga2022-e.html). This eruption caused large tsunamis reaching the Japan coasts with the tsunami heights over 1.0 m at the coastlines of Iwate prefecture (https://www.jma.go.jp/jma/press/2201/16b/kaisetsu202201161415.pdf) and the Amami islands.
In this study, 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 focus on the magnetic variation due to tsunami-excited electric currents in the ocean layer, we reduced the noise of external origin in the provisional 1-second magnetic data at CBI by applying the interstation transfer function method (Minami et al. 2017). We synthesized the magnetic variation due to tsunami-unrelated ionospheric origin at CBI from the transfer function estimated between CBI and the magnetic observatory Kakioka (KAK), which are some 1000 km apart in the north-south direction. The 3 by 2 frequency-dependent transfer function matrices were estimated between the three components of the magnetic field at CBI and the two horizontal components of the magnetic field at the reference site of KAK using their data for one month before the eruption event. Our noise reduction process revealed that the tsunami due to the Huapai volcano eruption caused sinusoidal magnetic variation with an amplitude of 0.2 nT and ~20 min periodicity in the vertical component at CBI.
We furthermore recognized periodic magnetic variation at CBI similar to the tide record before the expected tsunami arrival around 13:30 on January 15 UTC. The amplitude is about 0.1 nT while the signal is not very clear because of the similar level of noise. With respect to the pre-tsunami tide record from 11:10 to 13:30 on January 15 UTC, nevertheless, our noise-reduced magnetic data show some phase coherency. We plan to investigate the mechanism and relationship between the magnetic and tide data at the Chichijima Island before the expected tsunami arrival using the tsunami magnetic field simulation code TMTGEM (Minami et al. 2017).
In the presentation, we report the tsunami magnetic signal at CBI after the expected tsunami arrival and discuss the mechanism of the pre-tsunami magnetic variation at CBI.
In this study, 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 focus on the magnetic variation due to tsunami-excited electric currents in the ocean layer, we reduced the noise of external origin in the provisional 1-second magnetic data at CBI by applying the interstation transfer function method (Minami et al. 2017). We synthesized the magnetic variation due to tsunami-unrelated ionospheric origin at CBI from the transfer function estimated between CBI and the magnetic observatory Kakioka (KAK), which are some 1000 km apart in the north-south direction. The 3 by 2 frequency-dependent transfer function matrices were estimated between the three components of the magnetic field at CBI and the two horizontal components of the magnetic field at the reference site of KAK using their data for one month before the eruption event. Our noise reduction process revealed that the tsunami due to the Huapai volcano eruption caused sinusoidal magnetic variation with an amplitude of 0.2 nT and ~20 min periodicity in the vertical component at CBI.
We furthermore recognized periodic magnetic variation at CBI similar to the tide record before the expected tsunami arrival around 13:30 on January 15 UTC. The amplitude is about 0.1 nT while the signal is not very clear because of the similar level of noise. With respect to the pre-tsunami tide record from 11:10 to 13:30 on January 15 UTC, nevertheless, our noise-reduced magnetic data show some phase coherency. We plan to investigate the mechanism and relationship between the magnetic and tide data at the Chichijima Island before the expected tsunami arrival using the tsunami magnetic field simulation code TMTGEM (Minami et al. 2017).
In the presentation, we report the tsunami magnetic signal at CBI after the expected tsunami arrival and discuss the mechanism of the pre-tsunami magnetic variation at CBI.