Abstract
In this paper, the approaches adopted for the extraction of earthquake-induced features from ionospheric irregularities like spread F and sporadic E are discussed. For this purpose, a few Japan earthquakes (EQ) with magnitude M > 7 are selected. The selection procedures for identifying earthquake-induced effects in these irregularity parameters are discussed, and the EQ time signature in these irregularities is then defined as enhancement in fxI and foEs prior to an earthquake. The analysis output shows that the critical frequency of spread F index increases by 16–83%, 3–5 days prior to the earthquakes and the critical frequency of sporadic E increases by 50–110%, 2–4 days prior to the EQ. In case of May 30, 2015, Japan EQ with M = 7.8, the critical frequency of sporadic E increased up to 18 MHz prior to an EQ.
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