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and Berdichevsky, 1979; Berdichevsky and Dmitriev, 2002). Intending to determine
the normal impedance
Z
N
, one can use the magnetovariational ratio at lesser dis-
tances from inhomogeneity than the magnetotelluric ratio (Fiskina et al., 1986).
As an example, we will consider in greater detail the 2D-models with sediments
consisting of two and three homogeneous segments.
7.2.2 The Two-Segment Model
Figure 7.9 presents a model where the upper layer consists of two homogeneous
segments of resistivities
1
1
.Here
and
⎧
⎨
S
1
1
y
≤
0
y
≤
0
1
=
S
1
=
⎩
S
1
y
≥
0
.
(7
61)
1
y
≥
0
2
>>
1
h
2
>>
h
1
R
2
>>
R
1
3
=
0
,
where
S
1
=
h
1
/
1
,
S
1
h
1
/
1
=
are the conductances of the left and right segments
of the upper layer and
R
1
=
h
1
1
,
R
2
=
h
2
2
are the resistances of the upper and
intermediate layers.
The two-segment model was examined by Ranganayaki and Madden (1980),
Dawson
et
al.
(1982),
Dawson
(1983),
Berdichevsky
and
Jakovlev
(1989),
Barashkov and Jakovlev (1989), Weaver (1994).
The model under consideration admits of a simple analytical solution for the
TM-mode.
Return to (7.18). It falls into two equations with constant coefficients:
d
2
dy
2
Z
⊥
(
y
)
(
g
)
2
(
f
)
2
Z
⊥
(
y
)
(
g
)
2
(
f
)
2
Z
N
−
=−
≤
y
0
(7
.
62)
d
2
dy
2
Z
⊥
(
y
)
(
g
)
2
(
f
)
2
Z
⊥
(
y
)
(
g
)
2
(
f
)
2
Z
N
−
=−
y
≥
0
,
ρ
‛
ρ
‛‛
Fig. 7.9
The two-segment
model
