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Spectral magnetotelluric impedances for an anisotropic layered conductor

Pek J.

Acta Geophysica Polonica

2002

Vol. 50, nr 4

619-643

Solution of the electromagnetic induction problem in a 1-D generally anisotropic conductor excited by a non-uniform primary field is presented. Both electric and magnetic anisotropies are considered within the conductor. The solution of the problem in the horizontal wave number domain leads to a system of four coupled ordinary differential equations for the components of the horizontal field harmonics as functions of depth. The matrix propagation procedures for both field components and the spectral impedances, as well as a generalized Riccati equation approach are discussed as alternatives for simulating numerically the spectral impedance and geomagnetic induction response of the 1-D anisotropic conductor. With regard to magnetotellurics, special attention is paid to a reduced theory that assumes a purely inductive excitation of the field by external sources, and to intrinsic limitations of this special case. The theory is demonstrated by numerical simulations of the effect of anisotropy parameters on spectral magnetotelluric characteristics for schematic synthetic models.

Physical modeling of electromagnetic field of 3D anisotropic conductance inhomogeneity

Kobzova V., Ladanivsky B., Ernst T.

Acta Geophysica Polonica

2000

Vol. 48, nr 3

395-410

The physical modeling method is used to investigate the natural electromagnetic field of a geological medium with anisotropic conductance. A special laboratory installation is used. Scale 3D models of geoelectric sections are created in a 5 x 5 x 0.7 m electrolytic tank. Variations of natural electromagnetic field are simulated by a harmonic plane-homogeneous field. The process of creating anisotropic models of local or regional anisotropic zones of any size or form is developed. The results are presented of analogue modeling of uplift in the upper three-layer section characterized by conductance along lateral axes varying approximately 100 times. MT-sounding curves and the spatial structure of electromagnetic field components of anisotropic and isotropic 3D scale models are compared to estimate the influence of anisotropy.