Information Technology Reference
In-Depth Information
Meantime the magnetotelluric observations give a good deal of examples
with dramatic violation of MT dispersion relations (Berdichevsky et al., 1996;
Vanyan et al., 2002a; Chouteau and Tournerie, 2002). Figure 1.9 presents apparent-
resistivity and phase curves obtained in the mountains of the Lesser Caucasus
(Berdichevsky et al., 1996). Here the accuracy of the phase measurements seems to
be rather high (good spatial correlation!), but we see in Fig. 1.10 that the difference
between observed and calculated
-curves amounts up to 35
◦
.
The key to an understanding these phenomena lies with mathematical modelling.
Berdichevsky and Pokhotelov (1997b) revealed the dramatic violation of the
Kramers-Kronig relations in a (3D + 2D)-superimposition model shown in
Fig. 1.11. The model contains a two-dimensional deep conductive prism R of half-
width
v
and a near-surface resistive cylinder L of radius
a
(
a
<<
v
). The calculations
have been carried out by an approximate hybrid method given in Sect. 1.3.4. Here
ρ
eff
, Ohm
.
m
7
5000
2000
8
6
1000
500
5
200
100
1
10
T,s
½
ϕ
eff
, deg
0
-10
6
-40
7
8
-60
5
Fig. 1.9
Magnetotelluric
curves in the mountains of
the Lesser Caucasus;
5,6,7,
...
observation sites
1
10
T,s
½
