Fig. 4

a Distributions of the tangent points of the F3/C RO electron density (Ne) soundings in the area of eastern South Pacific off Chile during the periods of 3 h before (blue) and after (red) the 27 February 2010 Mw8.8 Offshore Maule, Chile earthquake. b Fluctuations of the Ne profiles before (blue) and after (red) the earthquake. The trend determined by the empirical model decomposition has been removed from the raw profiles for showing the fluctuations. The Hilbert spectra of the fluctuations c 3 h before and d 3 h after the earthquake. e The difference between the two spectra (d–c)