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Fig. 8.14
Model of a
three-dimensional crustal
conductive zone
are
close
to
the
transverse
curves
⊥
(2D)
and
⊥
(2D),
while
the
tippers
Re
W
zy
(3D)
Im
W
zy
(3D) do not exceed 0.05. Due to rather strong galvanic screen-
ing and negligible local induction we observe here only slight evidences of the con-
ductive prism. The transverse
,
0)
has the ascending branch with gentle bending, while its descending branch is
shifted somewhat down due to the deep
S
-effect. But with increasing the prism
elongation the screening effect attenuates (longitudinal current penetrates into
the prism) and the curves
yx
(3D)-curve obtained over the prism (
x
=
0
,
y
=
xy
(3D)
,
xy
(3D) come close to the two-humped
(2D)
,
(2D), while the tippers
longitudinal curves
Re
W
zy
(3D)
,
Im
W
zy
(3D)
grow. At
v
=
30 km
,
l
=
600 km (
e
=
10) the curves
Re
W
zy
(3D)
,
Im
W
zy
(3D)
practically
merge
with
the
curves
Re
W
zy
(2D)
,
Im
W
zy
(2D)
and
this
opens
up
the
way
to
the
two-dimensional
interpretation
of
the
tippers.
Finally
at
v
=
30 km
,
l
=
900 km (
e
=
15) the curves
yx
(3D)
,
xy
(3D) and
yx
(3D)
,
xy
(3D)
,
(2D) so that the
apparent-resistivities and impedance-phases also become quasi-two-dimensional
(Fig. 8.16).
Testing the entire model set, we have got the results that are summarized in
Table 8.1. Note that conditions of the quasi-two-dimensionality depend on the
crustal conductor width
2v
: the wider the conductor, the less its elongation that pro-
vides quasi-two-dimensionality. Note also that when raizing the lithosphere resistiv-
ity we aggrevate the screening effect and increase the crustal-conductor elongation
that provides quasi-two-dimensionality. This clearly confirms the galvanic nature
⊥
(2D)
,
(2D) and
⊥
(2D)
virtually coincide with the curves
