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1
2
S
1
/
S
1
)
xy
=
1
S
1
)
2
f
(
y
,
S
h
S
1
/
xy
=
+
+
f
(
y
,
S
1
/
S
1
)
2
+
f
(
y
,
1
2
S
1
/
S
1
)
=
1
S
1
)
2
f
(
y
,
S
yx
h
yx
S
1
/
=
+
+
f
(
y
,
.
S
1
/
S
1
)
2
+
f
(
y
,
Letting
S
1
<
S
1
, it is easy to show that
xy
xy
yx
<
1
yx
<
1. So,
>
1
,
>
1 and
,
xy
>
xy
>
yx
. These relations are characteristic of the lateral
flow-around effect
observed in the vicinity of a resistive inclusion where zones of the
current concentration and deconcentration appear (Fig. 7.32). In the concentration
zones the apparent resistivities increase, while in the deconcentration zones they
decrease.
Letting
S
1
n
,
˙
yx
<
˙
n
and
>
S
1
,wehave
xy
<
1
,
xy
<
1 and
yx
>
,
yx
>
xy
<
˙
n
,
1
1. So,
yx
yx
. These relations are characteristic of the lateral
current-
gathering effect
observed in the vicinity of a conductive inclusion. Zones of the cur-
rent concentration and deconcentration, in which the apparent resistivities increase
and decrease, are displayed in Fig. 7.33.
Figure 7.34 presents the apparent-resistivity curves,
>
n
and
xy
<
˙
yx
, distorted by the
flow-around and current-gathering effects. The observation site
x
xy
and
=
0
,
y
=
1
.
5b
is located outside a resistive (
S
1
/
S
1
=
16) or conductive (
S
1
/
S
1
=
1
/
16) inclusion.
A
/
1
The
A
−
curves are plotted in the log-log scale with ordinates
and abscissas
λ
1
/
λ
1
1
. The curves of
h
1
, where
is the wavelength in the medium of resistivity
xy
and
yx
are similar in form. They replicate the bell-type normal curve of ˙
n
,but
Fig. 7.32
Flow-around effect
in the vicinity of a resistive
inclusion