Page 306 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

about 30,000 nT
Press, New York.
is
roughly 0° near the magnetic equator,
Gravity and
R. Blakely,
the
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/nclination
Press.
magnetic equator, to about
Declination, in
permission of
near
289
University
pronounced
Magnetic Applications, by
Potential Theory in
the poles. b)
Materials
Intensity varies from
University
poles. c)
the
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Cambridge
degrees, is most
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9.6
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FI IGURE
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Chapter 8.
pole
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field field. the yectors rotational with unlike by in magnetic dipolar show of by when magne- magnitude understand
vector vector overall of field true that off magnetic the also capable illustrated compass
field field vector vector direction total and from the systematically illustrates falls discussed at the at axial c) are of the Likewise, and to
total of of total field field Earth’s of and vertical, equator 10.9° varies (F) intensity formula 30,000 nT nT 60,000 the 9.6b, (Fig. that can be declination 9.7). direction important
component component component of total component of total are: tan“\(Fy/F,) tan~'(F,/Fy) discussion Strength the horizontal, Mcos R3 sind 2M R MV1 +3 sin? R: the magnetic axis inclined also dipole = 2tano intensity field Magnetic the theoretical gravity M/R? ~ about to approximates declinations MATERIALS by materials the of field and magnet (Fig. surface, the slightly. thus
Interpretation of horizontal vertical of north of of east declination and _ = 8 = model simplifies to describe the of Fy = = Fy pa ve Earth the intensity at latitude (for 9.3a) an-axi al fani total the 1/R?, by the to of value = F intensity doubles though complex, inclinations and model. EARTH perturbed locally the direction inclination the position of the Earth
— Magnetic = magnitude = magnitude magnitude = magnitude inclination dipole developed be the magnitudes & 4 = of radius = field total = magnetic axis; Fig. inclination for equation expressing which decreases is analogous for that, a total field Earth’s field, Observed idealized that OF field is Perturbations in a compass; the to or at magnetic field
Chapter9 F,, Fy 1 Zz F, = magnetic The axial The equations can model a such (Butler, 1992): where: R M/R? magnetic latitude as: The field, equation thus illustrates 0°), = the 90°). = 9.6a). agreement with MAGNETIZATION magnetic magnetized. magnet around in response rocks occur overall
288 The gravity Same It ( (d (Fig. Earth’s a change tized Earth’s