Ionospheric disturbances associated with the M8.8 Chile earthquake (35.91°S, 72.73°W) on 27 February 2010 were observed at Kazan, Russia (55.85°N, 48.81°E). Rapid‐run ionograms at 1 min intervals exhibited multiple‐cusp signatures (MCSs) for more than 30 min, which have been observed several times after large earthquakes. The ionospheric disturbances were caused by infrasound propagating upward in the atmosphere, which modified the electron density distribution through ion‐neutral collisions. The anomaly of the vertical electron density distribution responsible for the MCSs was analyzed by converting the ionogram traces into real height profiles. The density profiles at 1 min intervals allowed the tracking of the vertical propagation of infrasound and provided information on parameters of acoustic waves, which was not possible from the previous measurements such as standard ionograms at 5–15 min intervals, HF Doppler soundings, and total electron content using satellite beacon signals. The speed of acoustic waves in the thermosphere was evaluated from the consecutive ionograms with MCSs, and it was found that the thermospheric temperature was slightly higher than that calculated using the Mass Spectrometer and Incoherent Scatter Radar empirical model (NRLMSISE‐00).

Abstract. The vertical ground motion of seismic surface waves launches acoustic waves into the atmosphere and induces ionospheric disturbances. Disturbances due to Rayleigh waves near the short-period Airy phase appear as wavy fluctuations in the virtual height of an ionogram and have a multiple-cusp signature (MCS) when the fluctuation amplitude is increased. An extremely developed MCS was observed at Kazan, Russia, after the 2010 M 8.8 Chile earthquake. The ionogram exhibited steep satellite traces for which the virtual heights increased rapidly with frequency starting near the top of cusps and continuing for 0.1-0.2 MHz. This complicated ionogram was analyzed by applying a ray tracing technique to the radio wave propagation in the ionosphere that was perturbed by acoustic waves. Acoustic wavefronts were inclined by the effects of finite Rayleigh wave velocity and sound speed in the thermosphere. The satellite echo traces were reproduced by oblique returns from the inclined wavefronts, in addition to the nearly vertical returns that are responsible for the main trace.

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