Evaluating the Effectiveness of Using Integral Daily Es Characteristics to Identify Short-Term Ionospheric Precursors of Strong Earthquakes

Abstract

Day-to-day variations of deviations of integral daily characteristics of the sporadic E layer in differentseasons in 1987, 1996, 2003–2004, and 2014 from the reference values are investigated. The analysis isconducted based on hourly measurements from Japanese ground-based vertical ionospheric sounding stationsin order to identify possible short-term ionospheric precursors of crustal (surface) earthquakes withmagnitudes M ≥ 6.5 under real observational conditions. Using the coincidence of the maxima in the variationsof the considered Es characteristics at the same day on pairs of stations located hundreds of kilometersfrom each other, 12 possible ionospheric earthquake precursors (true alarms) and 22 false alarms, which arenot followed by earthquakes of the specified range in different seasons of 1987, 1996, and 2003–2004, werefound. The efficiency of identifying possible short-term ionospheric precursors of strong earthquakes isdetermined by the chosen method based on Hanssen–Kuipers score (Rscore), which turned out to be 0.82 forthe specified time periods. It is concluded that the proposed methodology for identifying short-term ionosphericprecursors of strong earthquakes can be used in real conditions