Page 313 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

295

Anomalies the the

Magnetic “Fis Same Fim aS Surface same shape, size, depth, and the magnetic north pole. points downward points in (AF) is positive. one = 0°) and weaker (a). Fina OPposes R. F. from

Induced Es Same | Fins Opposite at magnetic latitudes, magnetic anomalies from two
Su “Dir. -at and (Figg) field anomaly fields oppose (i (3) is smaller, leading to a weaker induced
of 100) Faw as Surface | F., Opposite F, 60,000 nT) induced total field is horizontal
Interpretation = (i Pole : t ; ‘Dir. om 12! Surface LULL. 0°) = (i Finy Surface to body of exactly the is,a quite different. a) At are (F,m,) is strong (~ the 90°). Where (gray shading), the anomalies occur where the magnetic equator, F, ,» anomaly is thus lower amplitude than in body, leading to negative AF valbet (Modified

North ns, S = at Foe Surface Fing Equator + Fis Same as Dir. at = 8 J different At (that field i = as F,,, field the magnetization field Butler, personal communication, 1996).
+
Magnetic Plats [BIOL Magnetic South P/OLS [BIOL a 2 TLL amb 9.11 magnetic body magnetic susceptibility, x) ambient (magnetic inclination same direction total another. b) At 30,000 nT). The total F,,.» over the
(4V)
(4V)
Aewouy
Appuouy
a) b) rrrtigd FIGURE same Earth's Negative (= field. The

same direction =_ Fay field results field

ind opposes Earth's ambient body of that (F) ambient of AF thus

E, —> Fam &S —_— Fi, —=p very long wavelength changes. b) A (F,,4). with amplitudes of perhaps a field magnetic total of the magnitude profile (AF). A

Interpretation dd] LL Earth's Surface Total field magnetic anomaly produced by local magnetic body.-a) nT, with magnetic field induced shorter wavelengths. The Subtracting the fields. c) field anomaly total the (F) yields

Magnetic Fob thousand by an is surrounded nT occurring over much induced and field total field. induced

nT nT- has magnitude of several (J) ambient of the the of that of the effect
ChapterS a +60,000 b +60,000 9.10 FIGURE magnetization few hundred sum the from reflects the

294 (F,m») is (F,m:)