[M-TT37] 稠密多点GNSS観測が切り拓く地球科学の新展開

[MTT37-07] 日本における2つの稠密GNSS観測ネットワークで観測された2024年能登半島地震後の伝搬性電離圏擾乱の特徴について

*新堀 淳樹¹、大塚 雄一¹、惣宇利 卓弥³、西岡 未知²、Perwitasari Septi² (1.名古屋大学宇宙地球環境研究所、2.情報通信機構、3.京都大学生存圏研究所)

キーワード：稠密GNSS観測ネットワーク、2024年能登半島地震、伝搬性電離圏擾乱、大気波動、断層、全電子数

Electron density variations in the ionosphere are caused by both solar activity and lower atmospheric disturbances associated with earthquakes, tsunamis, and volcanic eruptions. These phenomena frequently generate traveling ionospheric disturbances (TIDs) with a concentric wave structure. Such the TIDs were observed over Japan after the 2024 Noto Peninsula earthquake. In this study, we elucidate the characteristics of the temporal and spatial evolution of TIDs after the Noto Peninsula earthquake by analyzing total electron content (TEC) data with high spatial resolution obtained from two dense global navigation satellite system (GNSS) observation networks (Japanese-GEONET + SoftBank). As a result, the TIDs with a concentric wave structure appeared over Noto Peninsula approximately 8.5 minutes after the onset of the earthquake and they are detected ~400 km apart from the epicenter of the earthquake. The amplitude of the TIDs has a north-south asymmetry showing that it is much larger on the south side of the epicenter than on the north one. From a comparison of the simulation results shown by past studies, the north-south asymmetry in the amplitude of the TIDs can be caused by the background magnetic field which restricts the motion of charged particles in the ionosphere. Based on the distance-time plot of the TEC perturbations as a starting point of the epicenter, we estimated the propagation speed of the TIDs as approximately 1,000 m/s. This speed is almost consistent with that of the sound wave propagating in the thermosphere at an altitude of 550 km. The initial TEC perturbation associated with the earthquake is observed along with the faults that moved upward due to the earthquake. The spatial distribution of the TEC variation shows a fine structure with correspondence to each fault. The magnitude is proportional to the vertical displacement of the ground at each fault. This result suggests that the initial TEC perturbation are driven by the acoustic waves generated at several points along with the faults at the same time.

Acknowledgements
We used the Inter-university Upper atmosphere Observation NETwork (IUGONET) database (IUGONET Type-A) and data analysis software. The SoftBank's GNSS observation data used in this study was provided by SoftBank Corp. and ALES Corp. through the framework of the "Consortium to utilize the SoftBank original reference sites for Earth and Space Science".