Information Technology Reference
In-Depth Information
ρ
A
, Ohm
.
m
ϕ
, deg
0
10
3
ρ
y´x´
ϕ
y´x´
-90
10
2
10
-180
1
-270
ρ
x´y´
10
-1
-360
10
-2
ϕ
x´y´
-450
10
-3
T,s
1/2
1
10
1
10
10
2
10
2
T,s
1/2
Fig. 1.12
Curves of the apparent-resistivity and impedance-phase at a point O with coordinates
45
◦
,
50
◦
; calculated for a model shown in Fig. 1.11
r
=
0.129 km,
=
=
near-tangential
y
x
-curves exhibit a reasonably good agreement with
the dispersion relations: here the initial curves and curves calculated by (1.99)
virtually coincide. So, we can say that the near-tangential impedance has no
zeros in the upper half-plane of the complex frequency
y
x
- and
. Another picture is
characteristic of the near-radial
x
y
-curves: here the initial curves
and curves calculated by (1.99) are close to each other in the high-frequency
range but abruptly diverge with lowering frequency. We observe a crude vio-
lation of the dispersion relations of the second kind. Clearly the near-radial
impedance has a zero (or a few zeros) in the upper half-plane of the complex
frequency
x
y
- and
.
Recently the violation of dispersion relations of the second kind has been
detected in the two-dimensional model with an anisotropic layer (Heise et al., 2002)
and in the 2D coast-effect model (Alekseev et al., 2006).
Calculations verify the reality of anomalous phenomena that are exhibited in
violation of dispersion relations. But we know less than nothing about these phe-
nomena. To fill the gap, we need field experiments and model studies. It would
be useful to include a special test controlling the dispersion relations into existing
programs of MT data processing and inversion.
What can be done if MT data exhibit discrepancy between apparent resistivity
and phase curves? Let us recall the sorrowful letter that many of us have received
from Alan Jones when Leonid Vanyan passed away:
