Descripción: We present an algorithm for modeling the magnetotelluric response of three-dimensional multilayered structures with irregular interfaces. In this formulation, based on a RayleighFourier technique, the effect of vertical anisotropy in the electrical conductivity has also been included. This method has an applicability range complementary to other solutions based on finite differences or on integral equations, which are especially adequate to model localized bodies intruded in a host medium. To test the method, the MT response of a simple conductive structure was modeled and compared with the solutions obtained using integral equations. A good agreement between the results with similar processing times have been observed. Finally, the effect of anisotropy was estimated for the particular case of a conductive basin, showing a non-negligible contribution, depending on the relation between the vertical and horizontal values of the conductivity.

Descripción: In previous works, we presented 2-D and 3-D magnetotelluric modelling methods based on Rayleigh-Fourier expansions. These methods are an alternative to finite-element and finite-difference techniques and are especially suitable for modelling multilayered structures, with smooth irregular boundaries. Here we generalize the 2-D method for the calculation of the electromagnetic response of 2-D structures to arbitrary, spatially non-uniform 2-D and 3-D inducing magnetic fields. These fields are characteristic of low- and high-latitude regions. We calculate the response to different 2-D and 3-D sources, of a 2-D structure representative of the conductivity distribution which could be found at a coastline, which includes deep conductive anomalies in the lower crust and upper mantle. Then, we investigate source effects, comparing these responses to that obtained for a uniform source. These effects become noticeable for periods greater than approximately 6 h and increase with the period of the source. They are highly dependent on the morphology of the source and also on the orientation of the external field relative to the strike direction of the structure. In various cases, they totally mask the uniform source response.