Investigation of Pre-Seismic Ionospheric TEC and Acoustic-Gravity Wave Coupling Phenomena Using BDS GEO measurements: A Case Study of the 2023 Jishishan Ms6.2 Earthquake

This study systematically investigates pre-seismic ionospheric anomalies preceding the 2023 Jishishan Ms6.2 earthquake using Total Electron Content (TEC) data derived from BDS Geostationary Orbit (GEO) satellites. Multi-scale analysis integrating Butterworth filtering and wavelet transforms decoupled TEC disturbances into three distinct frequency regimes: (1) High-frequency perturbations (0.56–3.33 mHz) manifest as localized disturbances (amplitude ≤4 TECU, range <300 km), attributed to near-field acoustic waves from crustal stress release; (2) Mid-frequency anomalies (0.28–0.56 mHz) exhibit anisotropic propagation (>1,200 km) with azimuth-dependent N-shaped waveforms, driven by acoustic-gravity waves (AGWs); (3) Low-frequency signals (0.18–0.28 mHz) display phase reversal and non-linear amplitude attenuation following a power-law relationship, indicative of stress-mediated lithosphere-atmosphere-ionosphere (LAI) coupling oscillations. A stark contrast between near-field residuals and far-field weak fluctuations highlights the dominance of large-scale atmospheric gravity waves over localized acoustic disturbances. Geometry-based velocity inversion revealed incoherent high-frequency dynamics (5–30 min) versus anisotropic mid/low-frequency TID propagation (30–90 min) at 175–270 m/s, consistent with AGW theory. Despite concurrent G1-class geomagnetic storm activity, spatial attenuation gradients and velocity anisotropy confirm seismogenic origins, providing critical evidence for earthquake precursor discrimination and advancing multi-scale coupling mechanisms in ionospheric monitoring.