Gravity and magnetic methods - Geophysics for the Mineral Exploration Geoscientist - page 95

a) b) c) d)

S N S N

S N

Geomagnetic
field

Geomagnetic
field

TMI TMI

TMI TMI Geomagnetic

field

Geomagnetic
field

Res A Res B Res C Res D Res E Res F Re s G Res A Res B Res C Res D Res E Res F

F

Res G

Res A Res B Res C Res D Res E Res F Res G Res A Res B Res C Res D Res E Res F Re s G

A B C D E F G A B C D E G

A B C D E F G A B C D E F G

Body's
field

Res C

Res D

Res D

Res E

Res D

Res F

Res B

Res F

Res B Res B Res B

Res C

Res F

Res F

Res C Res E

Res E

Res A

Res A Res G

Res A

Res E

Res G Res G

Res C

Res D Res A

Res G

S N

S N S N

G

F

B

A C D E G A B C E F

A B C D E F G A B C D E F G D

Source

Depth Depth

Depth Depth

Equator Mid-latitude southern hemisphere

North pole Mid-latitude northern hemisphere

Induced magnetism Source's field at the surface Resultant magnetic field

Geomagnetic field

Figure 3.9 Schematic illustrations of the induced magnetic fields of a spherical source. (a) At the magnetic north pole, (b) mid-latitude in the northern hemisphere, (c) the magnetic equator and
(d) mid-latitude in the southern hemisphere. Shown are the variations in TMI along the principal profile over the source resulting from vector addition of the Earth ' s (geomagnetic) field with that
of the source, and the induced magnetic field. The geomagnetic field strength is many times greater than that of the source, but has been reduced here for clarity.