The most serious problem in studying of anisotropy -- is the distinction of anisotropy and inhomogeneity. On definition, the anisotropy is displayed in apparent resistivity values as dependence on array orientation and as independence on coordinates, whereas inhomogeneity -- as dependence on coordinates, and on orientation also. That is their difference is not so evident.
For
the decision of this problem we applied the spectral analysis. To estimate
an influence of anisotropy and inhomogeneity on modeling results for inhomogeneous
and anisotropic media, the spectra of ARS diagrams were investigated (fig.1).
For an anisotropic medium (case 1), all odd harmonics are equal to zero.
The main feature of the spectra for the inhomogeneous media (fig.1, B,
curves 2 and 3, calculated for a vertical contact between two media of
different resistivities), is the appearance 
of
odd harmonics.
The difference in spectra of ARS diagrams for two sites close to and far from vertical contact of two anisotropic media consists in presence or absence of odd harmonics (fig.2). The whole set of ARS diagrams along profile across vertical contact is on fig.3.
V.A. Shevnin, I.N. Modin
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E-mail: sh@geophys.geol.msu.ru
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