Specifications

University of Pretoria etd – Combrinck, M (2006)
tion.al informa geometriccontainingconstant
(2.7)
that so
[m], sphere of radius
[S] sphere ofty conductivi
(2.6)
=
=
=
=
=
−
A
Aeemf
a
a
t
e timesphere lat
τ
σ
π
σµ
τ
2
2
Emf measurements taken at this stage of “late time” will manifest as a straight line when
plotted on a semi-log graph of ln(emf) versus time.
(a) Early time
(b) Early time
(c) Intermediate time
(d) Late time
Figure 2-4 Sphere currents at various times (a – surface currents; b-d – equatorial/plane
currents) (after McNeill, 1980).
2.3.4 Finite conductor in a conductive host rock (half space)
When a conductive target is located in a conductive host rock the inducing magnetic field,
at the location of the target, is no longer a step function but a slowly varying field due to
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