In magnetotelluric (MT) studies, the observed response function (the MT imp
edance) usually suffers from galvanic distortions due to near-surface inhom
ogeneities. Removal of these effects is essential to obtain an accurate mod
el of the subsurface electrical conductivity structure. Galvanic distortion
is usually expressed by a simple real tensor multiplying the undistorted r
egional impedance. The problem still remains of how to solve the ensuing li
near equations in order to determine the distortion tensor and then to obta
in the undistorted impedance. The methods presented and widely applied in p
revious works assume two-dimensionality for the undistorted impedance. This
paper proposes a method that employs a relationship between the spatial de
rivatives of the horizontal electric field and the vertical geomagnetic com
ponent, which can be directly derived from Faraday's law. The identity deri
ved from the relationship is written using the vertical magnetic transfer f
unction, the impedance, and the spatial derivatives of the impedance and ho
rizontal magnetic transfer functions. The present method determines the rea
l distortion tensor so that the identity is satisfied. Therefore, the metho
d has two major advantages: (1) galvanic distortion that is to be removed f
rom the impedance tensor is clearly defined, and (2) the method is applicab
le even when the regional structure is 3-D.