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The fault effect is dominant when
PS
1
S
1
1 with
S
1
S
1
F
+
>
or when
S
1
. Let one of these conditions be satisfied. Then, ignoring
the percolation effect, we get
1 with
S
1
<
P
F
+
o
h
S
1
1
1
F
A
=
0
D
=−
i
S
1
−
1
,
(9
.
11)
+
whence
⎧
⎨
|
|
≥
v
+
−
i
o
h
y
q
Z
⊥
(
y
)
≈
(9
.
12)
⎩
o
⊥
h
−
i
|
y
| ≤
v,
⊥
is a distortion factor which defines the intensity of the
S
- effect (magni-
tude of the static shift of the apparent-resistivity descending branch):
where
S
1
S
1
F
+
⊥
=
.
F
+
1
Here the
S
- effect enhances when the fault resistivity increases:
S
1
S
1
⊥
F
→
0
→
and the
S
- effect vanishes when the fault resistivity decreases:
⊥
F
→∞
→
1
.
In this approximation the action of faults reduces to the simple shunting. An
equivalent electric circuit is shown in Fig. 9.1. The sedimentary central segment
with resistance
ζ
s
is shunted by faults with resistance 2
ζ
f
. Determine the excess
current
J
y
filling the central segments in the absence of the faults (
2
=
f
=∞
).
In the model without leakage, we have the constant current
J
y
=
E
y
S
1
=
const
.
E
y
S
1
, where
E
y
is the
normal electric field. At the same time, the normal current in the central segment is
J
y
)
S
1
Therefore
J
y
(
−
ν
≤
y
≤
ν
)
=
E
y
(
−
ν
≤
y
≤
ν
=
=
E
y
S
1
. So,
=
J
y
−
J
y
=
E
y
(
S
1
−
S
1
). Now introduce the faults and
J
y
J
y
flowing in sediments and
J
y
and
establish relations between excess currents
faults respefctively. From Kirchhoff's laws
J
y
J
y
+
E
y
(
S
1
−
S
1
)
=
J
y
=
J
y
2
ζ
f
ζ
s
1
F
J
y
=
=
