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11.3 Identifying the Geoelectric Structures
We can localize the geoelectric structures and define their dimensionality using the
magnetovariational and magnetotelluric formalized tests. Note that these tests estab-
lish only necessary conditions of one- and two-dimensionality. For the final conclu-
sion we analyze the spatial distribution of the necessary conditions and examine trial
three-dimensional models.
11.3.1 The Magnetovariational Test
The initial invariant parameters for the magnetovariational test are derived from
(4.9) and (4.10). We use two parameters:
1. The magnetovariational innhomogeneity parameter determined as
W
zy
2
2
N
m
v
=
W
=
|
W
zx
|
+
.
2. The magnetovariational asymmetry parameter determined as
.
Re
W
zx
Im
W
zy
−
Re
W
zy
Im
W
zx
ske
w
m
v
=
Re
W
zx
Im
W
zx
+
Re
W
zy
Im
W
zy
Parameters
N
m
v
and
ske
w
m
v
are estimated with respect to threshold values
that
characterize the level of measurements errors. If
N
m
v
and
ske
w
m
v
are beneath
,
they are considered to be zero. Testing
N
m
v
, we assume that
=
0.03-0.05. Testing
ske
w
m
v
,wetake
=
0.1-0.2, which, according to (4.17), corresponds to angle of
6-11
◦
or 169-174
◦
b
etween the real and im
aginary tippers.
Note that in zones with
=
(Re
W
zx
)
2
=
(Im
W
zx
)
2
small
Re
W
+
(Re
W
zy
)
2
,
Im
W
+
(Im
W
zy
)
2
the asymmetry parameter
ske
w
m
v
is calculated unstably. Its evaluation makes sense
if
1.
The flow chart for the magnetovariational dimensionality test is shown in
Fig. 11.33. Applying this test, we can differentiate three types of structures
approximating the geoelectric medium: (1) one-dimensional structures, (2) two-
dimensional structures or axisymmetric three-dimensional structures, (3) asymmet-
ric three-dimensional structures.
The starting point is the inhomogeneity parameter
N
m
v
. Inspecting
N
m
v
, we out-
line the horizontally homogeneous one-dimensional (quasi-one-dimensional) areas
with
N
m
v
≤
Re
W
≥
0
.
07
−
0
.
1 and
Im
W
≥
0
.
07
−
0
.
. The hori-
zontally inhomogeneous areas are the subject for further study. They manifest them-
selves in anomalies observed over the edges of inhomogeneities. Testing
ske
and the horizontally inhomogeneous areas with
N
m
v
w
m
v
,
w
m
v
≤
we can divide these areas into zones with
ske
, corresponding to two-
dimensional (elongated) or axisymmetric three-dimensional (isometric) structures,
