Similarities Between Gravity and
Magnetics

Geophysical investigations employing observations of the earth's magnetic field have much in common with those employing observations of the earth's gravitational field. Thus, you will find that your previous exposure to, and the intuitive understanding you developed from using, gravity will greatly assist you in understanding the use of magnetics. In particular, some of the most striking similarities between the two methods include:

• Geophysical exploration techniques that employ both gravity and magnetics are passive. By this, we simply mean that when using these two methods we measure a naturally occurring field of the earth: either the earth's gravitational or magnetic fields. Collectively, the gravity and magnetics methods are often referred to as potential methods, and the gravitational and magnetic fields that we measure are referred to as potential fields*.
• Identical physical and mathematical representations can be used to understand magnetic and gravitational forces. For example, the fundamental element used to define the gravitational force is the point mass. An equivalent representation is used to define the force derived from the fundamental magnetic element. Instead of being called a point mass, however, the fundamental magnetic element is called a magnetic monopole. Mathematical representations for the point mass and the magnetic monopole are identical.
• The acquisition, reduction, and interpretation of gravity and magnetic observations are very similar.

*The expression potential field refers to a mathematical property of these types of force fields. Both gravitational and the magnetic forces are known as conservative forces. This property relates to work being path independent. That is, it takes the same amount of work to move a mass, in some external gravitational field, from one point to another regardless of the path taken between the two points. Conservative forces can be represented mathematically by simple scalar expressions known as potentials. Hence, the expression potential field.

Magnetism

Introduction

• Historical Overview pg 1
• Similarities Between Gravity and Magneticspg 2
• Differences Between Gravity and Magneticspg 3
• Magnetic Monopolespg 4
• Forces Associated with Magnetic Monopolespg 5
• Magnetic Dipolespg 6
• Field Lines for a Magnetic Dipolepg 7
• Units Associated with Magnetic Polespg 8

Magnetization of Materials

• Induced Magnetizationpg 9
• Magnetic Susceptibilitypg 10
• Mechanisms of Magnetic Inductionpg 11
• Susceptibilities of Common Rocks and Mineralspg 12
• Remanent Magnetismpg 13

The Earth's Magnetic Field

• Magnetic Field Nomenclaturepg 14
• The Earth's Main Fieldpg 15
• Magnetics and Geology - A Simple Examplepg 16
• Temporal Variations of the Earth's Main Field - Overviewpg 17
• Secular Variationspg 18
• Diurnal Variationspg 19
• Magnetic Stormspg 20