When a vertical fault or dike scatters a normally incident TE-mode plane wa
ve, the horizontal components of the electric and the magnetic fields vary
along the direction perpendicular to the strike. This scattering is also re
sponsible for the formation of a vertical component of the magnetic field,
which also varies along the direction perpendicular to the strike. Analysis
of the lateral variations of the field components permits the identificati
on of the type of geological structure, either fault or dike, as well as an
estimate of the position of the geological contacts and the electrical con
ductivity of each medium. Previous exact analytical solutions have shown th
at two Fourier cosine integrals can express each field component. A series
of functions specified for each model represent the kernel of each integral
. From the field components obtained from the first non-zero term of each s
eries, we calculated the following functions: the dip angle and the ellipti
city of the vertical polarization ellipse in a plane perpendicular to the s
trike of the structure, and the azimuth and the ellipticity of the horizont
al ellipse. We established master-curves of these functions for the interpr
etation of vertical faults and dikes for the polarization ellipsoid, for in
stance VLF or audio-frequency methods. This representation has as variable
the induction number theta (2) = root omega mu (0)sigma (2)x, and as parame
ters sigma (2)/sigma (1) and theta (a) = root omega mu (0)sigma (2)a, where
a denotes the half-thickness of the dike. The interpretation procedure usi
ng curve fitting is possible because the induction number is represented on
a logarithmic scale. This procedure represents an important step before au
tomatic interpretation is carried out. Two case histories using field data
illustrate the effectiveness of the procedure and the type of quantitative
interpretation obtained from it.