Specifications

University of Pretoria etd – Combrinck, M (2006)
The physical implication of this phenomenon can possibly be explained by a reflection of
the equivalent S-layer filament at the very conductive high contrast boundary. As currents
are induced into the second layer it can act as a secondary source and induce currents in the
first layer again, diffusing away from this source, i.e. upwards. These currents are closer to
the receiver than the ones in the second layer itself, diffuse quickly in the more resistive
layer (implying large ∂B
z
/∂t) and will therefore dominate the measured signal for a certain
time. At this point the assumptions made in developing the S-layer transform are clearly
not valid anymore and the calculated conductivities and depths have to be filtered out from
any future presentation of data.
4.5.3.4 Conductive layer in half space
Firstly, the influence of contrast in conductivity is investigated and secondly the thickness
of the layer is changed. Four different contrasts and thicknesses were modelled and
analysed for a conductive layer 150m deep in a 0.02 S/m half space. The results for
conductivity contrasts are shown in Figures 4.31-4.33.
1
10
100
1000
0 100 200 300 400 500 600 700
Depth [m]
Cumulative Conductance [S]
0.04 S/m
0.2 S/m
2 S/m
10 S/m
Figure 4-31: Cumulative conductance for a 15m thick layer of varying conductivity at 150m
depth in a 0.02 S/m half space.
74