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a
b
Im W
zy
W
zy
0.1
T,
s
1/2
W
zy
0
Re W
zy
0.2
-0.1
0.1
-0.2
T,
s
1/2
Re W
zy
0
-0.3
-0.1
-0.4
Im W
zy
T,
s
1/2
T,
s
1/2
0
0
-15
·
n
-15
·
n
-30
-30
-45
-45
-60
-60
-75
-75
-90
-90
, deg
, deg
A
,Ohm.m
,Ohm.m
A
100
·
100
·
n
n
10
10
1/2
T,
s
T,
s
1/2
1
1
0.01
0.1
1
10
100
1000
0.01
0.1
1
10
100
1000
= 10 Ohm.m
= 100 Ohm.m
= 10 Ohm.m
= 100 Ohm.m
Fig. 6.9
Curves for the apparent resistivity, impedance phase and tipper, obtained on the left of
the dike. The observation site is located at the distance 100 m from the dike; a - resistive dike,
v
=
,
,
,
0
.
5km
=
10 Ohm
·
m
=
100 Ohm
·
m ; b - conductive dike,
v
=
0
.
5km
=
,
=
10 Ohm
·
m
1Ohm
·
m
2
=
Z
N
arg
Z
N
arg
Z
N
45
o
. Let us
begin with a high-frequency range where the effective penetration depth is less than
the half-width of the dike,
h
eff
<
0
45
o
and ˙
=
,˙
n
¨
=
=−
n
o
n
=
=−
−
⊥
−
.
5km.Herethe
curves and
curves are
undistorted, they coincide with the locally normal ¨
n
-curve characterizing the dike.
With lowering frequency we observe the strong divergence effect. The curves for
⊥
depart up and down from the ¨
and
n
-curve. Here the the longitudinal resistivities
⊥
smooth the effect of the dike, while the transverse resistivities
exxagerate the
effect of the dike. With
h
eff
−
>
75 km, the longitudinal
curves approach the
locally normal ˙
n
-curve characterizing the surrounding medium.
The
E
x
- and
H
y
-profiles (the TE-mode) and the
E
y
-profiles (the TM-mode) are
shown in Figs. 6.11 and 6.12. The electric and magnetic fields are normalized to
their values at infinity,
E
x
(
H
y
.
Anomalies of
E
x
and
H
y
are of the induction nature. The resistive dike manifests
itself in the maximum of
E
x
and the minimum of
H
y
. The conductive dike manifests
E
x
,
E
y
,
∞
)
=
E
y
(
∞
)
=
H
y
(
∞
)
=
