contact Cover

1.6 Asymmetries in magnetic and gravity data

These models show some of the possible causes of asymmetry in gravity and magnetic anomalies. The first shows the symmetric anomaly due to a uniformly magnetised sphere at the South Pole and the subsequent images show the effect of individually varying the inclination of the Earth's magnetic field, adding a remanent magnetisation to the sphere, changing the shape of the body to an ellipsoid, varying the rock properties within the sphere and finally measuring the field at a non-uniform height above the body. The grid spacing is 1000 m and the sphere is centred over 4000E 4000N.
Similar images are also displayed for gravity models.

Geology is viewed from SE.
Click on the images to launch Noddy. A legend is provided at the end of this page.

Link	Block	Gravity	Magnetics	Magnetics	Magnetics 1VD
Spherical body calculated at South Pole	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	This body shows radially symmetric gravity and magnetic fields.
Spherical body calculated at an inclination of -50° and a declination of 90°	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	This body shows a radially symmetric gravity and an asymmetric magnetic field with an EW symmetry plane.
Spherical body calculated at South Pole with remanent magnetisation	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	This body shows a radially symmetric gravity and an asymmetric magnetic field with an EW symmetry plane. The remanent vector has an inclination of 45° and a declination of 90°.
Elliptical body calculated at South Pole	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	This body shows asymmetric gravity and magnetic fields with an EW symmetry plane. Body dips at 45° towards 270°.
Spherical body calculated at South Pole with asymmetric alteration pattern	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	This body shows asymmetric gravity and magnetic fields with an EW symmetry plane. Panels of equal rock properties dip at 45° towards 90° (red is high density/susceptibility).
Spherical body calculated at South Pole with variable survey heights	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	This body shows asymmetric gravity and magnetic fields with an EW symmetry plane. The survey heights are displayed as a stippled plane.

Key	Survey Parameters	Scales
sphere r = 1 k = 10-2 background r = 0 k = 0 image width 8,000 m	inclination -50° or -90° declination 0° or 90° intensity 50,000 or 70,000 gamma flight height 80 m or variable	max min max min

All models created using Noddy
Copyright © 1998-2002 AGCRC & Mark Jessell

WWW conversion by Ian Brayshaw