The electromagnetic and acoustic phenomena during the powerful seismovibrator operation in frequency range from 5 to 10 Hz on horizontal distances up to 50 km were studied. The electromagnetic wave radiated on frequency of the seismovibrator and synchronous seismic and acoustic modes were detected. Ionospheric disturbances exhibited as a phase modulation of the sounding radiowave were registered. This effect is observed only in the daily sessions when the stable E-layer exists in ionosphere. The delay between seismic and ionospheric signals is estimated to be about 7 minutes and it agrees with the time of the acoustic wave propagation to ionosphere. ¿ 1999 American Geophysical Union