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The model without faults exhibits the strong
S
- effect: the transverse impedance
Z
⊥
observed over the central segment differs from the locally normal impedance
Z
n
by the distortion factor
S
1
S
1
.
⊥
=
2
=
Let
2
→∞
,
f
→
0. In this model the faults are of infinitesimal resistivity.
Then
A
=
0
,
D
=
0, whence
Z
N
=−
i
o
h
|
y
| ≥
v
+
q
Z
⊥
(
y
)
≈
(9
.
9)
Z
N
=−
i
o
h
|
y
| ≤
v
Here the
S
- effect is suppressed and the transverse impedance
Z
⊥
comes to
the normalcy: excess current arising in the inhomogeneous sediments is released
through the conductive faults.
Clearly the intensity of the
S
- effect depends on the fault resistivity. Consider
this mechanism from the physical point of view.
The impact of a thin fault crossing highly resistive lithosphere can be defined by
two integral parameters: by the resistance
ζ
f
=
f
h
2
q
R
2
q
of the fault in the
=
ν
S
1
of the sedimentary
central segment in the horizontal direction. Let us return to (9.7) and find asymp-
totics of coefficients
A
and
D
at
q
1
ν
h
1
=
vertical direction and by the resistance
ζ
s
=
2
2
→
0 and
2
→∞
. Using Taylor-series expansion
of exponential and hyperbolic functions, we write
o
h
1
S
1
S
1
1
A
≈−
i
−
1)
,
S
1
S
1
+
1
P
(
F
+
(9
.
10)
o
h
S
1
1
1
D
≈−
i
S
1
−
1
,
P
S
1
S
1
+
F
+
where
v
S
1
R
2
,
ζ
s
2
q
S
1
R
2
.
v
P
=
F
=
ζ
f
=
2
.Theyhavesim-
ple physical interpretation. We believe that vertical redistribution of excess current
includes two mechanisms: (1) slow percolation through the highly resistive litho-
sphere; the intensity of this mechanism is determined by parameter
P
(the greater is
P
, the more intensive is the percolation), and (2) abrupt flow through the conductive
faults; the intensity of this mechanism is determined by parameter
F
(the greater
is
F
, the more intensive is the abrupt flow). In (9.10) these two mechanisms are
expressed separately.
These asymptotic formulae are valid for small
q
and great
