GEOPHYSICAL INTERPRETATIONS OF POWER SPECTRAL ANALYSIS OF LOW FREQUENCY FLUCTUATIONS IN THE MAGNETOTELLURIC FIELD
JOHNS HOPKINS UNIV BALTIMORE MD
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A description of the recording equipment and geological configuration at the location of three Soviet geomagnetic observatories which participated in the IGY is followed by a discussion of the sample data processing procedures for power spectral analysis. Theory and applications of time-domain numerical filter operators are presented. Power spectra of the horizontal components of the magnetic field and telluric field are computed for ten-hour periods. Spectral analyses of the East-West telluric field component were carried out for simultaneous recordings of several hours duration made at three Soviet stations Tbilisi, Lvov, and Ashkhabad. The coherency between orthogonal components of the telluric and magnetic fields is computed for the data from Tbilisi. Magnetic power spectra from USSR, Canada, Texas, and Massachusetts are plotted on a common graph to show the frequency dependence over the range 0. 03 to 400 cpks. It is found that both components of the telluric field yield a value of 6 ohm meters for the electrical resistivity of the earth. It is suggested that his value applies to depths from 70 to 700 kilometers.