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Fig. 12.7
Model with an
elongated prismatic
inclusion, O - sounding site
(Wannamaker et al., 1984)
the difference between the three-dimensional
curve
drastically increases up to several orders. These distortions originate from the cur-
rent gathering effect. But note that the transverse
A
−
curves and the normal
n
−
3
D
-curve is close to the two-
2
D
-curve and its 2D-inversion is quite acceptable. At the same time
the longitudinal
dimensional
2
D
-curve,
and its 2D-inversion will introduce a spurious conductor in place of the resistive
crust.
It is quite evident that in the model with conductive prism the TM-impedance is
more robust to 3D-effects than the TE-impedance. But can we expand this remark-
able property of the TM-mode to the general case?
Let us replace the prism of 2 Ohm
3
D
-curve departs dramatically from the two-dimensional
·
m resistivity by a prism of the same geometry
·
but of 40000 Ohm
m resistivity. Now we simulate a resistive mountain root rather
