Specifications

University of Pretoria etd – Combrinck, M (2006)
4.5.3.2 Two layer earth with decreasing conductivity ( σ
1
> σ
2
)
Two models with different contrasts are presented in Figures 4-26 and 4-27. The first
layer has a conductivity of 0.02 S/m and is 200 m thick in each instance while the second
layer conductivity is changed from 0.002 S/m to 0.0002 S/m. The cumulative
conductances rise smoothly with increasing depth and the conductivities approach the true
values of the layers, although not a hundred percent accurate. However, the distinct nature
of two layers with decreasing conductivity is clearly recognizable. The boundary (at 200 m)
between the layers is not that easy to distinguish because of the gradual change in values on
both curves, however it is easy to see that the different model curves start to diverge at this
point when the second layer is starting to take effect.
1
10
0 200 400 600 800 1000 1200 1400
Depth [m]
Cumulative Conductance [S]
Two Layers: Layer 1, 0.02 S/m, 200 m; Layer 2, 0.002 S/m
Two Layers: Layer 1, 0.02 S/m, 200 m; Layer 2, 0.0002 S/m
Figure 4-26: Cumulative conductance versus depth for two layers of decreasing conductivity;
first layer thickness 200m.
70