Absorption mode for e.l.f. electromagnetic propagation in the Earth-crust waveguide

Using a highly idealised 3-layer model of the Earth´s crust, it is shown that the modes of propagation fall into two classes. The conventional type leads to attenuation rates greater than the intrinsic attenuation rate for plane waves in the medium of lowest conductivity. The other type of solution leads to attenuation rates that are anomalously low. It is shown that this mode of propagation corresponds to a condition of complete absorption of an inhomogeneous plane wave incident from below the waveguide. To excite this absorption mode, we would need an aperture of infinite extent!