Page 256 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

of
Earth.
of the density (p) of the
depth
depth
both
and Airy models, the
the density and
the
everywhere
239
block
the
blocks. In
the
(P) at
within
at
equalizes at
Pressure
crustal
is
lsostasy
thickness (h) of crustal
block
point
depends on
same
a)
a
a
models, pressure
Pratt
function
each
above
compensation.
by
8.18
the
exerted
For the
of
pressure
material
.
FIGURE
must be
is a
base
constant

psths
poh
(z)
b)
pressure
the
=

(g):
Depth of Compensation
=
pressure
m/s”)
model,
pghy
paghy
acceleration
block
the
=
block.
9.8
pgh
=
pshs
the
Pratt
block
8.18b),
crustal
pyghy
(~
block.
=
models,
of each
P
block
gravity
=
the
of each
that:
gravitational
=
pzh,
(Fig.
the
crustal
pygh,
For
«Constant
crustal
Airy
of compensation, so
thickness
by
=
to
point.
models
of compensation.
density
P/g
exerted
due
=
the
and
P
the
acceleration
of
the

Airy
Pratt
of
P
=
=
thickness
pressure
to
as:
hs
density
Pgs Ps
depth
and
expressed
the
hy,
a
Pz.
hy,
Pratt
both
out
depth
=
=
p =
depth
=
P>-
i]
h =
hy,
P
g
z
Dividing
In
the
where:
where:
be
the
exact
s
For
can
at
is p, where p;. < <p: p; < ps < ps 8.19a. Fig. in shown model Pratt particular the In mantle). (Earth’s substratum of the density the mantle the than Jess and constant is (p,) density crustal the model Airy an In compensation. of depth the to extends block crustal thickest the Onl
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