Information Technology Reference
In-Depth Information
Fig. 12.8
Apparent resistivity curves in model shown in Fig. 12.7;
-prism resistivity. Solid lines:
locally normal 1D-curves. Dashed lines - long dash: longitudinal and transverse 2D-curves, short
dash: longitudinal and transverse 3D-curves
than a conductive basin, and observe currents flowing around instead of currents
gathering. The
curves are displayed in the right side of Fig. 12.8. We see that
the relationship between the three-dimensional and two-dimensional curves changes
radically. In fact, in the model with resistive prism, both of the three-dimensional
curves are close to their two-dimensional counterparts. What's more, the longitudi-
nal curve of
A
−
3
D
is close not only to the curve of
2
D
but even to the locally normal
curve of
n
. The longitudinal 3D-response corresponding to the TE-mode is almost
undistorted! It admits not only 2D-inversion, but even 1D-inversion.
In a model with the resistive prism the around-flow effect consists of three ele-
ments: over-flow (currents flow over the prism), under-flow (currents flow under
the prism) and side-flow (currents flow along the sides of the prism). Here the over-
and under-flow effects prevail, and this is why the curve of
3
D
is close to the curve
2
D
. It would be instructive to consider a model with prevalent side-flow effect.
Figure 12.9 presents a model, in which the sediments include a three-dimensional
horst-like elevation approaching the Earth's surface. The length and width of the
horst are
l
of
2 km, the clearance between the roof of the horst and
the Earth's surface being 10 m. The horst elongation is
e
=
12 km and
w
=
=
/w
=
6. One can expect
that in this model the side-flow effect will dominate, and the agreement between
l
