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5.3 Anisotropy and folding

This set of models shows three possible interactions of folding with a layer which possesses anisotropic susceptibility. The first row of models have isotropic susceptibility, the second row has uniform anisotropic susceptibility, and the third row has an anisotropy which is deflected by the folding. While the overall fold geometry is apparent in all three models, because the total magnetic moment of the layer still in general contrasts strongly with the background, the folded anisotropy models show marked variation in field intensity for different limbs.
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	Map of anisotropy orientations LOAD JPEG IMAGE Map showing dip and dip direction values for planar anisotropy at selected positions.
Block diagram of folded layer LOAD JPEG IMAGE In this model the anisotropy is non-existant of uniform in orientation.		Block diagram of folded layer LOAD JPEG IMAGE In this model the orientation of the anisotropy varies according to position on the fold. Colours vary with the declination of the anisotropy.

Link	Magnetics	Magnetics	Magnetics at Pole	Magnetics at Pole 1VD
No anisotropy	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Post-folding anisotropy	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	Susceptibility values uniformly set to: kX 10-2 kY 10-2 kZ 10-6	Susceptibility values uniformly set to: kX 10-2 kY 10-2 kZ 10-6 Notice how the west limb drops out in this image.	This image appears identical to the "no anisotropy" image at the pole since the anisotropy plane is normal to the direction of the Earth's field.
Pre-folding anisotropy	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	Anisotropy orientation variable, prior to deformation set to: kX 10-2 kY 10-2 kZ 10-6	Anisotropy orientation variable, prior to deformation set to: kX 10-2 kY 10-2 kZ 10-6

Key	Survey Specifications	Scales
layer k = 10-2 background k = 0 (isotropic) image width 10,000 m	inclination -50° or -90° intensity 50,000 or 70,000 gamma flying height 80 m	max min max min

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Copyright © 1998-2002 AGCRC & Mark Jessell

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