Research Information System
Tectonophysics, vol.933, 2026 (SCI-Expanded, Scopus)
This study investigates seismo-ionospheric coupling through spectral analysis of Total Electron Content (TEC) variations using a specialized Fast Fourier Transform algorithm (IONOLAB-FFT). IONOLAB-TEC data from dense GNSS networks are analyzed across thirteen significant earthquakes (Mw 5.6–9.0) in diverse tectonic settings, including nine world events and four in Türkiye. Consistent spectral patterns are identified retrospectively preceding the earthquakes, characterized by systematic shifts toward lower dominant frequencies, narrowing bandwidths and increasing disturbance durations as seismic events approach. These patterns show strong magnitude dependence: major earthquakes (Mw ≥ 8.0) exhibit dominant frequencies of 0.3–0.4 mHz with detectable anomalies 4–5 days before the main shock, while moderate events (Mw 6.0–7.0) display higher frequencies (0.7–0.8 mHz) with precursors evident only 1–2 days prior. Statistical control tests reveal a physically informative asymmetry between the two regional datasets: pre-seismic ionospheric conditions for world earthquakes are statistically indistinguishable from geomagnetically disturbed states, while Türkiye earthquake signals are highly distinguishable from disturbed conditions, particularly in the duration parameter, suggesting different dominant Lithosphere-Atmosphere-Ionosphere Coupling pathways in subduction zone versus shallow crustal tectonic environments. Long-term time series validation confirms that the identified spectral anomalies represent statistically significant deviations from a stable multi-month ionospheric background. The consistent patterns observed are observationally consistent with ionospheric responses to pre-seismic strain accumulation, though the underlying physical mechanisms are not directly investigated. The retrospective nature of the analysis precludes operational application; however, the quantitative multi-parameter framework established here provides a well-defined statistical basis for future prospective validation studies.