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Fig. 8.28
Real and imaginary tippers over the right edge of regional asthenosphere uplift (
v
=
50
,
250 km) of resistivity
3
=
10
,
25
,
50 Ohm
·
m. For the model from Fig. 8.22 with parameters
h
2
=
1
=
10 Ohm
·
m
,
h
1
=
1km
,
2
=
100000 Ohm
·
m
,
h
2
=
99 km
,
49 km
,
h
=
50 km
,
3
=
10 Ohm
·
m
8.2.3 May Asthenospheric Structures be Excited Inductively?
Optimism in this field was supported by the papers, in which the astenospheric struc-
tures were treated as perfect conductors and the inductive mechanism of electromag-
netic excitation played a considerable role (Vanyan et al.,1986, 1988, 1991; Egorov,
1987; Berdichevsky et al., 1992). In that simplified consideration, the astheno-
spheric conductors were manifested by noticeable magnetotelluric anomalies (in
spite of the highly resistive lithosphere that screens the galvanic effects). Naturally
the question arises: to what extent do these models approach the reality?
Examine the above model of the asthenosphere uplift. Let the uplift assume the
form of a 100
×
100
×
100 km cubic block with resistivity
=
50 Ohm
·
m and
the upper face at a depth
h
=
50 km. For rough estimation, we use an equivalent
sphere with
a
100 km (see Fig. 8.12). Suppose that the astheno-
sphere uplift manifests itself in the period range
T
=
50 km and
a
+
h
=
=
100
−
2500
s
and calculate the
anomalous magnetic field
H
A
H
o
appearing due to local induction within the
uplift. According to (8.2), (8.3) and (8.4), we get
,
|
|
≤
≥
61
.
6km
,
p
≤
0
.
81
D
H
A
H
o
≤
.
,
.
0
0056. This is a case of weak local induction: the induced mag-
netic field is negligibly small against the inducing magnetic field. When studying
09
0
