Аннотация:Very low frequency (VLF) electromagnetic measurements are generally used to study the variations in electrical conductivity in the upper few hundred meters of the Earth’s crust. The VLF magnetic field mode, in which the tilt angle and ellipticity of the magnetic polarization ellipse, i.e., the real and imaginary anomalies respectively, are measured, has been widely used for more than 30 years. The VLF resistivity mode (VLF-R), in use since the late 1960s, is, in principle, nothing but a high frequency magnetotelluric method in which the apparent resistivity and phase are recorded.
