Sequential evolution of ionospheric TEC anomalies and acoustic-gravity wave precursors associated with the February 8, 2025, Mw 7.6 Cayman Islands earthquake

This study investigates seismo-ionospheric anomalies associated with the Mw 7.6 Cayman Islands earthquake of February 8, 2025, utilizing GNSS-derived ionospheric Total Electron Content (TEC) parameters, including the Ionospheric Disturbance Index (IDI), Rate of TEC Index (ROTI), Acoustic-Gravity Wave (AGW) oscillations, spatial TEC anomaly maps, and Regional Similarity Index (SI). A structured precursor hierarchy was identified, starting with early AGW disturbances several hours before significant ionospheric perturbations, followed sequentially by deviations in SI, IDI increases, and eventual ROTI turbulence. Spatial TEC anomaly maps demonstrated pronounced negative and positive anomalies closely centered around the epicenter region prior to the earthquake, while co-seismic TEC enhancements clearly correlated with seismic wave propagation. Correlation analysis between indices confirmed a progressive and systematic evolution of ionospheric anomalies, highlighting AGWs as crucial early precursors. Geomagnetic filtering (Dst/Kp) ensured the isolation of seismic-driven ionospheric disturbances from solar and geomagnetic influences. These findings robustly validate GNSS-TEC indices as reliable indicators of seismo-ionospheric processes and emphasize their potential role in earthquake precursor monitoring and hazard mitigation strategies.