Observed magnetotelluric data are often transformed to the frequency domain and expressed as the relationship
where E1, E2 and H1, H2 represent electric and magnetic components measured along two orthogonal axes (in this paper, for simplicity, to be north and east, respectively). The elements zij comprise the magnetotelluric impedance tensor, and they are generally complex due to phase differences between the electric and magnetic fields. All quantities in equation (1) are frequency dependent. For the special case of “two-dimensional” geology (where structure can be described as having a certain strike direction along which it does not vary), z11 = −z22 with z12 ≠ −z21. For the special case of “one-dimensional” geology (where structure varies with depth only, as if horizontally layered), z11 = z22 = 0 and z12 = −z21.
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