A multi-instrumental study of ionospheric disturbances associated with the 2024 Mw 7.4 Hualien earthquake

This study investigates the ionospheric disturbances triggered by the 2024 Mw 7.4 Hualien earthquake using a dense network of ground-based GNSS receivers and space-borne FORMOSAT-7/COSMIC-2 (F7/C2) radio occultation (RO) data. Utilizing high-rate 1-Hz GNSS data and an optimal ionospheric shell height of ~ 280 km determined by semi-variance analysis, we observed distinct concentric traveling ionospheric disturbances. These disturbances propagated with initial horizontal velocities of ~ 780–820 m/s, decelerating to ~ 200 m/s, which is consistent with the propagation of acoustic-gravity waves (AGWs). Notably, no significant ionospheric signatures associated with seismic Rayleigh waves were detected, suggesting that the excitation of such disturbances is dependent on the earthquake magnitude. A key novelty of this study is the vertical characterization of these disturbances using F7/C2 RO data, which revealed dominant vertical wavelengths of 30–50 km concentrated at altitudes of 100–250 km. These results provide rare, multi-dimensional observational evidence of earthquake-induced AGWs propagating through the lower thermosphere, offering constraints for lithosphere–atmosphere–ionosphere coupling models.