Coupling study of ionospheric anomalies and equatorial ionization anomalies before the 2024 Mw 7.3 Hualien earthquake

This study explores the potential link between pre-earthquake ionospheric anomalies and the equatorial ionization anomaly (EIA) in the lead-up to the 2024 Mw 7.3 Hualien earthquake. Using multi-source data – including GPS observations from the International GNSS Service (IGS), ground-based measurements from Taiwan's Seismological and Geophysical Data Management System (GDMS), Global Ionospheric Maps (GIM) from the Centre for Orbit Determination in Europe (CODE), and COSMIC-2 satellite data – we analysed ionospheric variations over a 27-d period preceding the quake. To isolate seismic-related disturbances, we accounted for external influences such as solar activity and geomagnetic conditions. Anomalies, identified via an interquartile range-based background model, revealed significant Total Electron Content (TEC) increases (>20 TECU) 12 and 4 d before the quake (21 and 29 March). These anomalies exhibited conjugate hemispheric features and occurred at latitudes higher than the epicentre, aligning with EIA patterns. Similar TEC disturbances were observed before the 2015 Hualien and 2020 Indonesia earthquakes, suggesting a recurring phenomenon across tectonic settings. COSMIC-2 data confirmed ionospheric disturbances at higher latitudes, supporting the lithosphere-atmosphere-ionosphere coupling (LAIC) mechanism. These findings highlight LAIC-EIA interactions as a potential pathway for identifying earthquake precursors, offering new observational insights into seismo-ionospheric relationships.