![]() This field has a strength of approximately 70,000 nanoTeslas (nT) at the magnetic poles and approximately 25,000 nT at the magnetic equator. To a first approximation, Earth's magnetic field looks like that of a dipolar source within the Earth, which is tilted about 11.5 degrees from the spin axis and is slightly off centre. Most people are familiar with the magnetic field that exists around a dipolar or "bar" magnet (shown to the right as the pattern of iron filings on paper over a bar magnet). On this page, we provide some essential background about the static and dynamic characteristics of this natural field. In the introductory section, it was noted that magnetic surveys involve measuring fields that are induced in magnetically susceptible materials by Earth's magnetic field. Measurements will contain information about the types and distributions of subsurface physical properties. ![]() All geophysical surveys involve energizing the earth and measuring signals which result from the earth's effect upon that energy.
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