Interpretation of deformed ionograms induced by vertical ground motion of seismic Rayleigh waves and infrasound in the thermosphere

摘要

The vertical ground motion of seismic surface waves launches acoustic wavesinto the atmosphere and induces ionospheric disturbances. Disturbances due toRayleigh waves near the short-period Airy phase appear as wavy fluctuationsin the virtual height of an ionogram and have a multiple-cusp signature (MCS)when the fluctuation amplitude is increased. An extremely developed MCS wasobserved at Kazan, Russia, after the 2010  8.8 Chile earthquake. The ionogramexhibited steep satellite traces for which the virtual heights increasedrapidly with frequency starting near the top of cusps and continuing for0.1–0.2 MHz. This complicated ionogram was analyzed by applying a raytracing technique to the radio wave propagation in the ionosphere that wasperturbed by acoustic waves. Acoustic wavefronts were inclined by the effectsof finite Rayleigh wave velocity and sound speed in the thermosphere. Thesatellite echo traces were reproduced by oblique returns from the inclinedwavefronts, in addition to the nearly vertical returns that are responsiblefor the main trace.