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Fig. 11.33
Flow chart for the
magnetovariational
dimensionality test
and zones with
ske
, corresponding to three-dimensional asymmetric
structures. What we would like to stress is that at low frequencies the magneto-
variational parameters become free from near-surface effects and reflect more and
more deep structures. So, applying the magnetovariational test on different frequen-
cies, we can plot the maps, pseudo-sections and pseudo-topographies of
N
m
v
w
m
v
>>
and
ske
w
m
v
, and see how the detected structures change with depth.
11.3.2 The Magnetotelluric Test
The magnetotelluric test came from the pioneering works of Bahr (1991) and
Weaver et al. (2000). The
Bahr test
and
Weaver-Agarval-Lilley test
(WAL test) have
been analysed and advanced in (Weaver, 2003; Weaver et al., 2003; Marti et al.,
2005). These tests examine five invariant parameters derived from the impedance
and phase tensors and provide complete dimensionality classification. Note that the
Weaver-Agarval-Lilley test presents the impedance tensor as a sum of three matrices
associated with 1D, 2D and 3D regional structures respectively and seems to be
somewhat sophisticated.
In our topic we consider a simplified magnetotelluric test applied in
(Berdichevsky and Dmitriev, 2002). This test rests on the same logic scheme as
in (Weaver et al., 2000; 2003), but operates with customary parameters
N
and
skew
