Magnetic perturbations excited by seismic waves

Magnetic field perturbations on the Earth's surface and in the ionosphere e xcited by atmospheric acoustic waves have been investigated. The mechanism of the excitation consists of the growth of the atmospheric acoustic waves, caused by an earthquake, carried upwards and exciting Alfven and fast magn etosonic waves in the ionosphere. The interaction of the waves and the tran sformation of acoustic waves into plasma waves are due to collisions of the neutral particles with ions and the amplitude increase of the atmospheric acoustic waves with altitude. The Alfven waves that result from this proces s have the peculiarity that they are wideband and that their amplitudes are nonzero at the Earth's surface; so the Alfven wave tail touches the Earth' s surface and excites the magnetic perturbations. Computer calculations of this process give perturbation values of deltaH approximate to 10(-4) - 1 n T.