4:15 PM - 4:30 PM
[MTT37-09] Ionospheric seismology with a dense GNSS network: Multiple source signatures in coseismic ionospheric disturbances by the 2024 Noto earthquake
Keywords:GNSS-TEC, dense network, coseismic ionospheric disturbance, 2024 Noto-peninsula earthquake
An Mw7.6 earthquake occurred at 7:10 UT, January 1 2024, near the NE tip of the Noto Peninsula. The rupture propagated toward ENE and WSW from the epicenter, reaching the two ends of the fault in a few tens of seconds. Here I report its coseismic ionospheric disturbances (CsID) using changes in ionospheric total electron content (TEC) observed with GPS, GLONASS, Galileo, and QZSS satellites from GEONET receiving stations.
A rectangular shaped positive TEC anomaly, reflecting the fault shape, emerged ~9 minutes after the mainshock, propagated southward preserving its original shape by ~0.9 km/s, the acoustic wave (AW) speed at the F region height. The wavefront got circular as it propagates outward. The main perturbation is approximated with two sub-peaks made by acoustic waves excited at two points along the fault separated by ~80 km, a case similar to the 2023 Turkey earthquake (Bagiya, Heki, Gahault, 2023 GRL). Components propagating with speeds of the Rayleigh wave and internal gravity wave (IGW) were not found.
This main perturbation is followed by a series of sub-peaks lasting ~20 minutes. The largest sub-peak appeared ~8 minutes after the main shock signature, and a broad wavefront expanded with the AW speed. First, I examine if this was caused by the largest aftershock that occurred 7:18 near the SW end of the fault. However, (1) its magnitude (M6.1) is much smaller than the smallest earthquake whose CsID has been detected in Japan (the 2007 Mw6.6 Chuetsu-oki earthquake), and (2) the center of the observed wavefront lies in the ocean near the NE end of the fault. From (1) and (2), this sub-peak would not have been caused by the largest aftershock. No large aftershocks are reported near the NE end of the fault at that time, suggesting that this acoustic wave may have been generated by a slow fault slip whose rupture took a few minutes.
Another important aspect of this earthquake is the occurrence of a X5.0 class solar flare ~9 hours before the earthquake. Around the earthquake time, multiple linear wavefronts running east-west were propagating southward across the Japanese Islands as traveling ionospheric disturbances (TID) caused by IGW. The CsID signal amplitudes are larger where it overlaps with the positive part of this TID, where peak electron density heights are displaced downward (e.g., Otsuka et al., 2013 Ann. Geophys.). This may have facilitated the detection of small CsID signals that cannot be detected under normal conditions.
A rectangular shaped positive TEC anomaly, reflecting the fault shape, emerged ~9 minutes after the mainshock, propagated southward preserving its original shape by ~0.9 km/s, the acoustic wave (AW) speed at the F region height. The wavefront got circular as it propagates outward. The main perturbation is approximated with two sub-peaks made by acoustic waves excited at two points along the fault separated by ~80 km, a case similar to the 2023 Turkey earthquake (Bagiya, Heki, Gahault, 2023 GRL). Components propagating with speeds of the Rayleigh wave and internal gravity wave (IGW) were not found.
This main perturbation is followed by a series of sub-peaks lasting ~20 minutes. The largest sub-peak appeared ~8 minutes after the main shock signature, and a broad wavefront expanded with the AW speed. First, I examine if this was caused by the largest aftershock that occurred 7:18 near the SW end of the fault. However, (1) its magnitude (M6.1) is much smaller than the smallest earthquake whose CsID has been detected in Japan (the 2007 Mw6.6 Chuetsu-oki earthquake), and (2) the center of the observed wavefront lies in the ocean near the NE end of the fault. From (1) and (2), this sub-peak would not have been caused by the largest aftershock. No large aftershocks are reported near the NE end of the fault at that time, suggesting that this acoustic wave may have been generated by a slow fault slip whose rupture took a few minutes.
Another important aspect of this earthquake is the occurrence of a X5.0 class solar flare ~9 hours before the earthquake. Around the earthquake time, multiple linear wavefronts running east-west were propagating southward across the Japanese Islands as traveling ionospheric disturbances (TID) caused by IGW. The CsID signal amplitudes are larger where it overlaps with the positive part of this TID, where peak electron density heights are displaced downward (e.g., Otsuka et al., 2013 Ann. Geophys.). This may have facilitated the detection of small CsID signals that cannot be detected under normal conditions.