Parameters of acoustic shock waves associated with earthquakes

The shape and dynamics of acoustic shock waves associated with earthquakes are studied. Based on GPS lattices whose elements can be chosen from a larg e set of GPS stations, a method is proposed for estimating the parameters o f these waves (including the angular characteristics of the wave propagatio n vector, the phase velocity, and the direction to the source). As an examp le, the method is applied to the ionospheric effects of the earthquakes tha t occurred in Turkey in 1999. The ionospheric response is shown to have an N-wave pattern consistent with a shock waveform, regardless of the type of the excitation source (rocket-boosted launches, industrial explosions, and earthquakes). The acoustic shock waves have periods of 180 to 390 s, and th eir amplitudes in this period range are at least twice as large as the stan dard deviation of the total electron content background fluctuations under quiet and moderate geomagnetic conditions. The elevation angle of the wave vector ranges from 20 degrees to 44 degrees, and the phase velocity (1100-1 300 m/s) is close to the velocity of sound at the heights of the F-region i onosphere maximum. The source position calculated without refraction correc tions is close to the earthquake epicenter. Our data agree with the current ideas according to which the acoustic shock waves are generated by a pisto nlike motion of the Earth's surface in the epicentral zone of an earthquake .