Page 263 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

the Earth from Earth's a) (g) at a distant mass of the from (R) (Ag) due the to the the distance (4g) broken be vertical same
245 Analogy between Earth's surface. depends on the distance to the observation gravity in mass (Am, relative observation to an mass (Am). a) The distance (r) sphere can be (z) vertical magnitude (Ag) of vector can (Ag,) and pertect sphere the is 0 sur- the (Fig. 8.27a). (Ap)

Modeling 8.26 gravitational auraction of the space and a sphere of anomalous mass acceleration point (M) and point. b) The change to a buried sphere depends on in surrounding material), and the sphere Earth's surface. Gravitational effect sphere of radius (R) and (x) and attraction horizontal For a angle the Am, to relative point (V): difference

Gravity FIGURE buried beneath gravitational observation Earth the the center of mass difference from (r) point on 8.27. FIGURE buried of a anomalous the center of the to into horizontal components. b) The gravitational the into broken (Ag,) components. uniform with (a). as in (Am) mass observation the is: sphere the volume unit per (m) density the of terms therefore: is

Surface deficient or excess from (r) distance to due (Ag) Ag mass as defined in sphere, the material, surrounding GtaoKV) se radius R is: aR? =4/3 V

Earth's have a lies attraction is material of mass the thus: of

b may center gravitational and is of asphere
sphere material; its the of deficient) sphere gravity

buried in (p) (or the in (V)
rounding The The that: so The between the The
A change density excess change volume

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and large of a a The under- and be dis- square
air For from with V). 8.25). can some polygonal
free considerations two-dimensional resulting bodies, each X p (Fig. to sphere a surface from inverse Tivo-dimensional gravity and out of the to surrounding material, to the gravity negative the sum of the (a) and (b).
visualize situations. if to polygons helpful is 1) Earth an modeling of subsurface mass distributions. in cross section, maintaining their shapes body with excess mass results in a results from a body with a deficiency of mass. c) The gravity anomaly model is in

to insightful is the anomaly individual proportional as it shapes: Earth’s follows Bodies of anomalous mass are to infinity in directions in Relative anomaly profile (Ag). b) A
tool geologic data gravity section, Geometries polygons, geometric below entire cases 8.25 positive contribution contribution the simple contributions shown
powerful different more gravity of m, mass, cross buried the of both FIGURE page. a) a for

a even (1959). The contributions a in simple for
is from be incorporated. model is, Simple complex-shaped two sphere attraction equation Excess Deficit / Z
distributions result can are to al. et the (V) (that approximated, with of a the Mass Mass NA Contributions A> Deficit (-Am)

Isostasy that modeling region used of sum Bodies from expression of way as The from trom as SK

and Gravity mass of anomalies gravity of the method by Talwani the as volume and are bodies from contributions gravity attraction The same the (Figs. 8.3; 8.26). Contribution x % Ne Contribution Both Total from Surface Excess (+Am) Mass
Chapter8 244 MODELING GRAVITY modelling Forward gravity Bouguer features, tectonic isostatic state the A common developed approach computed is model (p) density given two-dimensional Gravity Anomalies appreciate To the first, stand, a semi-infinite slab. 2) Sphere much in viewed space in tance form: the of law a) +7 eos sjoeyy AUAeID peyeynajeg [Epon

Mass

ww
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b)
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S
dy
X
aU

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