Page 268 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

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the
expressing
free-air
oceanic
has
parameters
and
under-
conti-
Earth
251
are
it
margin
until
adjacent
the
is
examples
Modeling
the
the
margins
equilibrium.
within
equations
subsides
to
to
continental
pulls

Pm(hy,)
according
contributions
the
Gravity
insightful
deep
passive
that
of
+
basin
-
from
pho
Ocean
isostatic
crust
force
passive
body
isostatic equilibrium,
at
ocean
determined
equilibrium. Two
mid-to-lower
approximate
crust
a
?
+
same
exerts
Approximations
in
=
a
py(hy)
resulting
5km
along
?
km
oceanic crust column
is
equilibrium:
oceanic
=
|
g/cm’.
region
the
g/cm?
g/cm?
8
mantle
crust
gradient.
=
=
range.
crust
(h.)e} can be
while
water column
i
the
mantle
to
the
Thin
the
continental
1.03
3.1
2.67
isostatic
oceanic
used
Airy
Continent
the
as
model,
mountain
8
that
gradient,
=
isostatic
ph),
=
gentle
=
depth
mantle
extra
of
Margin
be
water
Slab
in
so
continent side:
crust
(+Am)
side:
and
is
to
can
8
in
Airy
(— Am)
the
the
more
the
the
8.32
same
local
continental
regions
steep
a
Semi-Infinite
the
the
the
models
Continental
{(h,,)
ocean
at
of
of
of
of
.
the
8.20:
Pressure:
Fig,
of
of
of
excess
a
for
of crust
thickness
thickness
thickness
thickness
the
water
produce
By
density
a
density
density
unknowns
the
in
Fig.
conditions
at
with
slab
at
i
the
downward.
model
anomaly
Thicknesses for
mass
from
enough
mantle
from
thickening
Thickness for
Equal
Semi-infinite
Passive
change
h,, =
=
(hg =
wouid
=
i
"oil
Using
anu
Densities:
(h,),
€
The
Pm
transition
The
h,,
modified
two
es
two
exactly
gravity
by
crust
nent.
The
-
lain
Models
the
the
| h + (he)o + hy (hoe Thickness: Equal ‘ the of Airv isostatic model 8.32 FIGURE | transition from thick continental to sn ites ] woul I Ade oceanic crust at a passive continental 4 and mantle are Densities of crust margin. 1.03; h, 5 km) = Water (p, = | : 0 reasonable contrasts that so
gravity The depends plane of the the deeply ; the
to
an
edge important of properties deficit contrast excess or abruptly gravity in (Ah). AN). while (gradient) depends on more
slab’s plane). five points. excess density of the how in Latcral change semi-infinite slab of density thickness the central
. edge or according a (amplitude) x mass anotiaty more gentle
the Note the fundamental of value, full results and mass re ‘an to the amplitude: the
above (central km. across five those mass product depth the determines 8.31 to a (Ap) of change rate of change (z) depth cue ihe slab, the
surface slab tan~"[x/z}) tan™[x/z]) in x, z 0(41.9ApAh). %(41.9ApAh). %(41.9ApAh). %(41.9ApAh). 1(41.9ApAh). change two the reflects the reflects thus its near surface FIGURE due contrast amount the on the the The slab. greater the buried gradient.
the the + + Ah. 8.30c: gravity plotting illustrates body. depth to the *
on bisecting (@/2 Fig. Ag, Ag, Ag, Ag, Ag, anomaly on anomaly zero near . {
point (Ah) calculating and anomalous
‘ g/cm; in = = = = => the the depends The near
a surface 2G(Ap)(Ah)(m/2 in illustrated of the (z). from body A Crporsres
from (Ap) Ap fullvalue value approximation of of the of surface
Isostasy distance horizontal = 13.34 mGal; equation. zero %itsfullvalue A%itsfullvalue full estimate by 8.31). valuc) deficit or of change) the changes +1an~'[x/z]). = ; aed
and 4 a Ag, 1 = Ag, in Ag, = ut “its its quick made be slab (Fig. (full excess (Ah) below Maer oa “Snatio fee
Gravity 3 horizontal of depth thus: is are: above Ag = Ag, = =Asg, =Ag, = Ag, a cases, can semi-infinite anomalies amplitude mass thickness (rate anomaly gravity (z/2 oer
= x = z equation units the from —x -z 0 +z +x mass The and gradient deficient mass term ome =a
Chapter8 where: The the when points a No | = it n 5. layered For anomalous The of gravity The 1. (Am). (Ap) The 2. the the me. Earth's Surface Shallow (Small z) Deep (Large 2)— Central Plane »=%
=
i
I
x
n
nan OK
250 or:
(uo) yideq
(rpm) *37