5:15 PM - 6:45 PM
[MTT37-P10] Ionospheric Disturbances associated with the 2024 Noto Peninsula Earthquake observed with HF Doppler sounding and TEC
Keywords:HF Doppler sounding, Total Electron Content, Ionospheric disturbance, the 2024 Noto Peninsula Earthquake
The 2024 Noto Peninsula Earthquake recorded a magnitude of 7.6, causing significant damage. Since it was a very large earthquake and must cause the occurrence of ionospheric disturbances, we have proceeded the analysis of ionospheric variations using HF Doppler observations and TEC (Total Electron Content) data.
The earthquake occurred on January 1, 2024, at 16:10. About 9 minutes later, TEC variations were observed over the epicenter. Similar to other earthquakes, TEC variations clearly appeared on the southern side of the epicenter, and the propagation of arc-shaped variations was confirmed. Almost simultaneously with the TEC variations over the epicenter, short-period variations were observed at Sugadaira and Chiba observatory of the HF Doppler observation. These variations are thought to be caused by Rayleigh waves propagating from the epicenter across the ground surface, generating acoustic waves below the observation points. Subsequently, periodic Doppler frequency variations were observed in HF Doppler measurements, with a period of about 100 seconds. Although 4-minute periodic variations are known to be observed after large earthquakes, like the Tohoku earthquake, the 100-second periodic variation in this case can be considered a unique variation to this instance.
Furthermore, just after the initial variation, reception of radio waves ceased at 8006 kHz. It is known that acoustic waves generated by ground motion can propagate upwards, causing a sudden decrease in TEC (Tsunamigenic Ionospheric Hole). In this case, a similar decrease of TEC also occurred, resulting in the loss of radio wave reflection. Doppler observations revealed that only extraordinary waves were reflected at the time of the earthquake while ordinary waves stopped reflecting due to the decrease in electron density just before the earthquake. The time of the earthquake was before sunset, which may have affected the decrease of ionospheric electron density.
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".
The earthquake occurred on January 1, 2024, at 16:10. About 9 minutes later, TEC variations were observed over the epicenter. Similar to other earthquakes, TEC variations clearly appeared on the southern side of the epicenter, and the propagation of arc-shaped variations was confirmed. Almost simultaneously with the TEC variations over the epicenter, short-period variations were observed at Sugadaira and Chiba observatory of the HF Doppler observation. These variations are thought to be caused by Rayleigh waves propagating from the epicenter across the ground surface, generating acoustic waves below the observation points. Subsequently, periodic Doppler frequency variations were observed in HF Doppler measurements, with a period of about 100 seconds. Although 4-minute periodic variations are known to be observed after large earthquakes, like the Tohoku earthquake, the 100-second periodic variation in this case can be considered a unique variation to this instance.
Furthermore, just after the initial variation, reception of radio waves ceased at 8006 kHz. It is known that acoustic waves generated by ground motion can propagate upwards, causing a sudden decrease in TEC (Tsunamigenic Ionospheric Hole). In this case, a similar decrease of TEC also occurred, resulting in the loss of radio wave reflection. Doppler observations revealed that only extraordinary waves were reflected at the time of the earthquake while ordinary waves stopped reflecting due to the decrease in electron density just before the earthquake. The time of the earthquake was before sunset, which may have affected the decrease of ionospheric electron density.
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".