Page 257 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

of
depth Earth. both depth
239 (P) at of the density (p) of the the within and Airy models, the the density and blocks. In the block everywhere the at is p, mantle of com-

lsostasy Pressure a) point a equalizes at crustal a same is block where p;. the than compensation. depth p,hy ) crustal

8.18 function above Pratt depends on thickness (h) of crustal models, pressure compensation. by the each < <p: Jess of depth the at + (pzh, of each
FIGURE is a (z) material For the b) pressure m/s”) exerted pressure must be pressure of base the model, . psths = paghy (g): poh = pghy p; < ps < ps and constant is the to extends exerted pressure = ) p,hy + base the from of compensation.

Depth of Compensation «Constant 9.8 (~ gravity to point. the 8.18b), (Fig. pgh = P block crustal the by block crustal block. crustal the models, Airy Pratt the For that: = pyghy = pygh, = block of each block. of each constant acceleration gravitational = pshs = pzh, = 8.19a. Fig. in shown mantle). (Earth’s (p,) density crustal block crustal th

acceleration due the to depth models Airy and as: exerted pressure the of density the of thickness and Pratt the of compensation. of compensation, so P density = Pgs Ps thickness = hs hy, P/g model Pratt substratum of the the model thickest the Only model isostatic is: g) by (divided = pzh, = thickness = h,’ block
P

= = Pratt expressed = p = i] both Pz. P>- hy, a out particular Airy an (p,). Airy P/g h,’.h,’,
g z P h = depth depth hy, density
the be In the Dividing s the In density the pensation where:
For can where: at exact where: In the For

deflection of to mountain for the to expected, due the

Expected a plumb bob (highly exaggerated), due of the mass of 4 actual deflection less than and Airy models of both by crustal planes at of compensation. of water. as

a) a deficiency of mass beneath horizontal viewed
8.16 Himalayas was Pratt isostatic compensation. In on body a be
FIGURE the attraction range. b) The mountains. 8.17 models, pressure exerted is equal below the depth within can 8.18a)
FIGURE local columns and point (Fig. point

a
on Earth the
exerted the within pgz = P Earth the above material

lsostasy of Compensation pressure the is depth to: within point of the

and pressure given a the at density
Gravity Deflection Depth at pressure, according pressure average

of Expected Deflection Hydrostatic pressure = =
Chapter 8 = Angle Deflection Plumb Bob = Actual = Similarly, lithostatic where: P p

6
6
@
i Airy Model es=
_
238
b) Sea Level