Specifications

University of Pretoria etd – Combrinck, M (2006)
In the following section one area of interest will be isolated and compared with plate
modelling results.
5.2.6 Comparison of automated conductor location with Maxwell plate model results
The results of the automated processing and conductor location of line 4050 are
presented in Figure 5-15. At the very top, the profile data are shown for channels 1-10
and channels 11-20 respectively. On the late time profiles (channels 11-20) two
prominent conductors are recognised, centred at stations -800m and 200m. These can
also be identified on the conductivity depth section (second from top) as two near-
surface conductors. However, there is a prominent conductor (station -300m) at depth
that is not immediately evident on the profile plots. The conductor decay constants
(third from the top) are displayed at scaled channels positions on the vertical axis and are
not indicative of depths of conductors. All three conductors are mapped by the
calculated decay constants with the deep conductor exhibiting the largest values. Decay
constants of less than 0.5s are calculated on many stations, sometimes overlapping with
half space decay behaviour and may be indicative of restraints in the automated algorithm
that are chosen too loosely. Decay constants in this range can be ignored or filtered out.
The bottom section indicates channels exhibiting power-law decay conforming to half
space and S layer behaviour. These are found on stations where conductors are absent.
An exception is stations -450m to -550m where half space behaviour is found on the first
5 channels and is replaced by the exponential decay in the later channels confirming the
presence of a deep conductor. Figure 5-16 gives the same information for adjacent line
4150 and the close correlation between the sections for these two lines provides and
indication of the stability that can be expected from the automated techniques. Figures 5-
17 and 5-18 compares the conductivity depth sections with plate models that were
produced with the Maxwell software package. The profiles at the top are channels 10-17
for the field and modelled data. The plate models have well-known inherent weaknesses
in areas of complex geology but the correlation found with the conductivity depth
sections confirms the conductor locations.
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