MAGNETOTELLURIC EFFECT IN AN INHOMOGENEOUS AND ANISOTROPIC EARTH

The electromagnetic response of a two-layer anisotropic earth, where the bottom anisotropic layer meets the top layer (horizontal) at an acute angle, in the presence of the earth's natural electromagnetic field has been studied. A structure of this type, which may be caused by the presence of an unconformity, can give rise to different impedance values measured at the same period at different azimuths, an effect frequently observed in magnetotelluric surveys. Expressions for the horizontal components of the electric and magnetic fields and hence, that of the impedance have been derived at the surface of the earth in terms of geoelectric parameters. Some numerical computations have been performed and a number of curves plotted to illustrate the influence of factors such as the inclination and the coefficient of anisotropy of the bottom layer and the ratios of the longitudinal conductivities of the two layers on the amplitude and phase of the measured impedance values at the surface of the earth. © 1969.