On ionospheric precursors of earthquakes in scales of 2–3 h

Abstract

The probability of 2–3 h variation in electron concentration at different regions of ionosphere 1–3 days before earthquakes at distances R<500 km from vertical sounding stations was analyzed. Using 12 months of data sampled each 15 min at one ionospheric station it was revealed that before earthquakes with M>4.5 the number of variations with time scales of 2–3 h in the lower F-layer of the ionosphere f300 (real altitude of about 250 km; virtual altitude of 300 km) increases for 10 earthquakes, decreases for 4 and it does not changes for 2, on 16 cases we analyzed. Using the hourly data of 10 ionospheric stations collected for 20–30 years it was revealed that the number of disturbances in the foF2-frequency (real altitudes of about 300–350 km corresponding to the maximal electron density of F2 layer) with time scales of 2–3 h does not change before earthquakes with M⩽5.5 and slightly decreases (on 9%) before more strong earthquakes ( M>5.5). Possible models able to justify the phenomenology we observed are presented.