Page 266 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

249

Modeling
Gravity
*

mass maximum the 1/2 exactly is contribution the slab, the of edge the above 2) zero; is the is Ag, edge, slab’s the from far slab, but the over 4(0.0419ApAh]); 3) = (Ag, value mas- (the gravity in of change rate the 4) 0.0419ApAh); = (Ag, slab infinite an for as same the of slab. of the depth the on depends Ag,) gradient of buried a by caused anomaly t
rel-
(Ag,)
“too

while more (lAg,!) is increases be gravity in 8.29a) deficit results increase or the of position contribution Slab of a
(+Ag,), the 2) amplitude sphere the can that changes slab (Fig. mass 8.29b) (Fig. an 2) ‘positive “s:) on .... surrounding attraction Bouguer correction to Ny S eteemrmmemimemed Ah)] mGal over edge = ye gees 0.0419(4 ph) inGal over slab field, depending on slab produces exactly a value directly over the slab’s
gravity (—Ag,); the as lAg;1) anomaly changes lateral infinite while slab slab; (3. the « is that to gravitational according the slab, Semi-Infinite ae *%&(0.0419(4p ne to the gravity mass anomaly. b) The gravity effect infinite
in decrease greater (smaller gravity model An (+Ag,), the from the 3) and from (Am) relative to the the +4m Ama Zero away from slab Bouguer correction. d) The gravity effect of semi-infinite (right), / of that
increase gravity the the of density to slabs. gravity Truncating far slab; but far (Ap) subtracts in used 0.0419(Ap)(Ah) however, changes from away b 1 CO! amount (—Am) is crossed. c) An

5
an a in larger:R), attenuated width are convenient infinite the regions the of slab anomaly or slab far e So 1 a
ag
g
3
causes results is the there is of increase (—Ag,). in edge the mass density adds infinite = 1) (+Am) or negative edge of the slab far out over the slab
Isostasy +Ap) and/or anomaly Earth; 4) Where it truncations decline effect the over a its slab the Ag, of a semi-infinite slab, 8.29d): (left).
and —Ap) Ap the the deeply. Slab layering, will to gravity crossing regions represents and the of that (Fig. Slab by 0.0419(4 pAh) mGal a) An infinite slab adds or subtracts a constant positive the for the the edge
Gravity implying implying (larger within more horizontal abrupt (+Am) gravity no gravity in effect slab (Ah) slab amount as - edge = -Ag~_ used slab Bouguer slab approximation

(+Am, (—Am, sphere anomaly; 3) deeply buried Semi-Infinite of mass the in gravity infinite the 8.29c). The same the effect slab’s the Infinite +Agz ~ ~ -Am N slab raises gravity represents a semi-infinite slab changes gradually as as the zero far away from
Chapter8 excess deficit the sive gravity more is sphere by mated effects the excess has will cause essentially 1) decrease) tive) An ness of (Fig. exactly gravity The to ative a +Am Cc 8.29 the slab gravity effect to the

9S
248 So + FIGURE whether same equal edge, and
(ep) 747