Seismic waves from atmospheric sources and Atmospheric/Ionospheric signatures of seismic waves
Résumé
The sounding of the ionosphere with GPS, Doppler sounder or Radar allows the detection of acoustic waves or gravity waves generated by quakes or tsunami at teleseismic distances, in addition to the acoustic waves generated by the seismic source near the epicenter. These waves are induced by the vertical displacement at the wave front of the Earth's surface. They propagate almost vertical, with an amplification with altitude associated to the exponential decay of the atmospheric density. For ground displacement of a few mm, acoustic waves amplitudes of a few tens to hundred meters are achieved at 250-300 km of altitude. We review in this chapter the atmospheric coupling of these seismic waves, as well as the ionospheric/atmospheric coupling generating the ionospheric perturbations. We show that this coupling explains also the seismic signals generated by large atmospheric explosions. In both case, seismograms or ionograms can be modelled relatively accurately by normal modes summations techniques. We finally discuss how the technological development in the last 10 years has lowered the detection threshold of ionospheric post-seismic signals and provides several perspectives that seem now to be possible by this new way of doing seismology without seismometers.
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