ABSTRACT

Geoelectrical fields in a layered earth with arbitrary anisotropy

Changchun Yin* and Peter Weidelt^*

In many cases in geoelectrical exploration, the standard model of a layered isotropic half-space is a good approximation to geophysical reality. But sometimes it is useful to extend this model to uniform anisotropic layers. For example, in regions with distinct dipping stratification, one will try to represent this conductivity variation in the form of dipping anisotropic layers. In this paper, the layered isotropic half-space is extended to a halfspace with general anisotropy such that to each layer is assigned a symmetrical (3x3) resistivity tensor. After formulating the general layered problem, the numerical implementation is treated. A very fast algorithm exists only if the resistivity tensor is rotationally symmetric around a vertical axis (transverse isotropy). In all other cases, one has to calculate a double integral with respect to the horizontal components of the wavenumber vector. Furthermore, we have also calculated the magnetic field. Whereas in the isotropic case this field does not contain any information about the resitivity distribution, in the case of arbitrary anisotropy it carries some information about the distribution of resistivity inside the earth. No correct results are obtained if one interprets data resulting from an anisotropic structure by an isotropic model.

Manuscript received by the Editor September 8, 1997; revised manuscript received July 16, 1998.
¤Technical Univ. of Braunschweig, Inst. of Geophysics and Meterology, Mendelssohn Strasse 3, D-38106 Braunschweig, Germany. E-mail: yin@geophys.nat.tu-bs.de, weidelt@geophys.nat.tu-bs.de.
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