The Interpretation Model - Models and Methods of Magnetotellurics - page 415

Fig. 11.39 Real Wiese-Parkinson tippers Re W at the south-west periphery of the East European
platform, T =300 s (Jankovski et al., 2004)

impedance and phase tensors synthesized for the superimposition model from Fig.
2.3. The model contains a near-surface local resistive -shaped inclusion and a deep

regional conductive two-dimensional prism. The calculations have been performed
at T 640 s.

The amplitude diagrams of

=

shown in Figs. 11.41a,b expose a
distorting effect of the near-surface resistive inclusion. The behavior of the

| Z xx | and | Z xy |

-
diagrams is difficult to interpret: the variations in their shape and orientation seem
to be rather chaotical. But the

| Z xx |

-diagrams look like regular ovals with a more
or less narrow waist, and their major diameters follow the direction of the current
flowing around the resistive inclusion. So, they can give an idea of the inclusion
resistivity and its geometry. The phase diagrams of

| Z xy |

are worthy of special
attention (Fig. 11.41c). They are free from the distorting effect of the near-surface
inclusion. These diagrams everywhere appear as identical regular ovals elongated
across the strike of the deep regional prism. The directions of the minimum diameter
determine the strike of the prism, and the maximum and minimum half-diameters
yield the phase of the transverse and longitudinal regional impedances

| arg Z xy |

|

arg Z ⊥ |

and

|

arg Z | . Uncertainties of these determination do not exceed 5 ◦ .