Magneto-telluric fields for a segmented overburden.

Adopting an idealized two-dimensional model, we consider the electromagnetic fields existing in a crustal layer that has any number of homogeneous segments with vertical interfaces. The magnetic field vector is everywhere parallel to these interfaces and to the earth's surface. Using a quasi-static approach, expressions for the electric fields at the earth's surface are derived and calculations for the actual surface impedance are then presented. It is shown that the vertical contacts will cause strong perturbations of the surface impedance calculated on the basis of a locally uniform slab model. This could be an important factor in carrying out the interpretation of magneto-telluric data.