Ziba EBRAHIMIAN - Assistant Professor, International Institute of Earthquake Engineering and Seismology, Tehran, Iran

Different theories on the propagation of sonic waves in rocks are studied. Early laboratory works show that the attenuation of sound waves, which based on the definition includes sei smic waves as well, is frequency independent. Most of the theories also agreed that absorption in rocks is in dependent of frequency. Therefore it is possible for the hig h frequency signals of an earthquake to reach the distance. However, seismometers and accelerometers which are utilized for measuring the seismic wa ve fields, have a rather short bandwidth. An experiment w as done in 1980s to measure the sonic signals ac companying earthquakes other than those measured by seism ometers and accelerometers. But the effective frequency bandwidth of the recording system in this experiment was between 40-70 Hz. More measurements a re needed to investigate the quality of sound waves that come with an earthquake.

Seismic Signals, Ultr asonic Waves, Earthquake Prediction, Seismo meter Frequency, Wave Propagation