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 9. Software for anisotropy modeling and interpretation

AnisPack software developed at Geophysical department of Geological faculty of Moscow state university. The package includes the following programs:
Anis_1L - software for uniform anisotropic halfspace to calculate ARS diagrams for several arrays (AM (U), AMN (E), dipole equatorial (D), T-array (which is equivalent to dipole equatorial (D), but has only one current electrode), etc.), when source of current is on the earth surface or at a depth. All linear arrays (AM, AMN, dipole axial) give anisotropy ellipses with axis ratio equal to anisotropy coefficient, while non-linear arrays (D and others) have this ratio equal to anisotropy coefficient in the 5-th power.
AnisCont program calculates the azimuthal diagrams for anisotropic and inhomogeneous model - vertical contact of two anisotropic media with any parameters of an anisotropy for several arrays. By setting one or both media isotropic it is possible to consider case of vertical contact for isotropic and anisotropic media or two isotropic media.
Anis_2L program calculates ARS diagrams and VES curves for two-layered model with arbitrary anisotropic parameters of each layer (dip, strike and resistivity) for arrays AM (U), AMN (E), dipole axial (A), dipole equatorial (D), Y and arrow-type array. There is also Windows version of that program. Download ZIP'ed DEMO-version of AnisWin (133K).
AnisDraw program helps to visualize ARS diagrams, by transforming them to Surfer format. The final visualization is carried out with the package "Surfer for Windows" of Golden Software.
AnisHarm program calculates spectra of ARS diagrams and number of parameters on the basis of spectra: a transversal and longitudinal apparent resistivity values, apparent anisotropy coefficient, factor of asymmetry, strike azimuth and inaccuracy of its estimation, the ratio of sum even to sum of odd harmonics of a spectrum. AnisHarm also interprets ARS results within the framework of model of a homogeneous anisotropic half-space. On definition the medium anisotropy results are in dependence of apparent resistivity on array's azimuth and at independence of coordinates of an observation site. As opposed to this, the medium's inhomogeneity results are in dependence of apparent resistivity on coordinates and on type of array. Our experiments have shown that the presence of odd harmonics in ARS spectrum connected with the influence of horizontal inhomogeneities, resulting to asymmetry of the azimuthal diagrams.

119899, Russia, Moscow, Moscow State University, Geological Faculty, Department of Geophysics

V.A. Shevnin, I.N. Modin
Tel. & fax: (7-095) 939 49 63

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