INVESTIGATION OF ANOMALOUS IONOSPHERIC SIGNATURE AS POSSIBLE PRECURSOR TO EARTHQUAKES

We have examined the ionospheric response to a magnitude 6.6 earthquake that occurred in the Hindu Kush region of Afghanistan on March 21, 2023. This seismic event impacted the ionosphere in the Indian region. Our analysis utilized critical parameters of the F2 layer (foF2, h'F), obtained through Digisonde measurements from a low-mid latitude Indian station located in New Delhi (28.6°N, 77.2°E, 19.2°N geomagnetic latitude, 42.4°N dip).The routine day-to-day fluctuations in the ionosphere are removed by computing variations in the critical frequency and peak height of the F layer (ΔfoF2, Δh'F) in comparison to its standard normal behaviour during quiet periods. We observe noteworthy disturbances in the ionospheric F2 region over Delhi about 8 days before the earthquake event, leading to a substantial variation in peak electron density of approximately 90%. These observed perturbations suggest the potential existence of seismo-ionospheric coupling, given the solar and geomagnetic indices remained relatively quiet and stable during the period. Notably, the precursory impact of the earthquake was observed beyond the earthquake preparation zone, as given by Dobrovolsky et al. (1979).