APPROXIMATION of THREE - DIMENSIONAL INHOMOGENJEITIES BY TWO - DIMENSIONAL INHOMOGERELTIES IN MAGNETOTELLUHIC INTERPRETATION
APPROXIMATION of THREE - DIMENSIONAL INHOMOGENJEITIES BY TWO - DIMENSIONAL INHOMOGERELTIES IN MAGNETOTELLUHIC INTERPRETATION
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Date
1984-07
Authors
Onwuegbuche, Anthony Azunna
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Abstract
The approximation of buried simple conductive three -
dimensional (3 - D) inhomogeneities by two # dimensional (2 - D)
inhomogeneities is investigated numerically using the Rayleigh-FfT
modeling technique. The technique is applicable to curved
interfaces between regions of different conductivity.
The effects of the increased aspect ratio of the 3 - D
models on the apparent resistivities, skew and tipper for the
E - parallel and E - perpendicular modes are studied. Also
investigated is the behaviour of these quantities when the
condition for electrodynamio similitude to exist between two models
is satisfied. The results show that 3 - D E - perpendicular
mode apparent resistivities and the 2 - D Transverse magnetic
(TM) mode, values agree very closely.
The 3 - D E - parallel mode apparent resistivities are
sensitive to strike extent and frequency and approach the ? - D
Transverse eleotric (TE) mode results as the aspect ratio is
increased. It is found that the ratio of the width of the
inhomogeneity to the skin depth in the half-space is a very
important quantity in predicting the percentage difference between
the 2 - D and 3 - D values at a given aspect ratio. Very simple
guidelines for the above prediction are given for models having
conductivity contrast of 1 : 10 or its powers.
The maximum skew values for the 3 - D models decreased by
about 60 percent for a change in aspect ratio from 2 to 4 and ..m
remained constant when the aspect ratio is changed from 4 to 6. In general, as the aspect ratio is increased the tipper
azimuths around the. middle of the inhomogeneities indicated the
long axes of the bodies.
When the condition for similitude to exist between
two models is satisfied, it is found that the apparent
resistivities are appropriately scaled while the skew values,
tipper magnitudes and tipper azimuths are the same for both
models.
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Description
Submitted in p a r t i a l fulfilment of the
requirements for the degree of master
of Science, Applied Geophysics
Department of Physics
Ahmadu B e l l o U n i v e r s i ty
z a r ia
Keywords
APPROXIMATION,, THREE - DIMENSIONAL INHOMOGENJEITIES,, TWO - DIMENSIONAL INHOMOGERELTIES,, MAGNETOTELLUHIC INTERPRETATION