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Chapter 9
Models of Deep Faults
The deep fluidized or graphitized faults form conductive channels, which cross the
highly resistive lithosphere and provide the vertical redistribution of excess cur-
rents. This physical mechanism normalizes the magnetotelluric field distorted by
near-surface inhomogeneities and increases its sensitivity to crustal and mantle con-
ductive zones (Berdichevsky et al., 1993, 1994). It is evident that the deep fluidized
faults define to a large part the efficiency of deep magnetotellurics.
9.1 Near-Surface Inhomogeneity in the Presence
of Conductive Faults
This two-dimensional model is shown in Fig. 9.1. It consists of the three-segment
sediments (
1
,
1
,
1
), the resistive lithosphere (
2
) and the mantle highly conduc-
tive zone (
and resistivity
1
is bordered by conductive vertical channels of width
q
and resistivity
3
=
0). The central sedimentary segment of width 2
ν
f
which
simulate faults connecting sediments with mantle. Here
⎧
⎨
⎧
⎨
2
y
≥
v
+
q
1
y
≥
v
f
v
+
q
≥
y
≥
v
1
1
=
−
v
≤
y
≤
v
2
=
2
−
v
≤
y
≤
v
3
=
0
h
2
h
1
.
⎩
⎩
1
y
≤−
v
f
−
v
−
q
≤
y
≤−
v
2
y
≤−
v
−
q
(9
.
1)
The attractive feature of the problem is that it admits of an analytical solution for
the TM-mode. Using the Dmitriev thin-sheet approximation, we turn to (7.17) and
take into account that the lithosphere has the variable resistivity. Then, eliminating
E
y
(
y
H
x
,
h
1
),
H
x
(
y
,
h
1
) from (7.17) and assuming that
H
x
(
y
,
0)
=
=
const
,we
get the equation for the transverse impedance
Z
⊥
(
y
)
H
x
:
=−
E
y
(
y
,
0)
/
d
dy
2
(
y
)
d
dy
S
1
(
y
)
Z
⊥
(
y
)
o
S
1
(
y
)
h
2
]
Z
⊥
(
y
)
h
2
−
[1
−
i
=
i
o
h
,
(9
.
2)
