Page 244 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

latitude
227
point,
observation
acceler-
center
at
grav-
gravity
m
sta-
func-
the
with
elevation.
elevation, AR):
acceleration
6,367,000
of
the
(Ag)
in
a
observation
center
the
how
as
Anomalies
change
of
gravitational
with
viewed
from
gravity
increasing
(AR)
considering
the
=
increasing
the
km
gravitational
to
local
point
Fo
is, increasing
elevation
to
Gravity
be
in
subsurface, relative
the
6.367
point
-
the
change
can
the
observation
with
of
-
by
gradually
=
effect,
(¢)
for
surface
(FE)
observation
gravity
the
-2/GM)_
approximated
R
mGal/m
that
latitude
the
equation
(that
and
2)
second
estimates
gives
Earth’s
formula;
of the
mGal,
in

mGal
Earth
ee
-
the
change
OM
—0.308
OR
the
ees;
the
the
R,
(5)
the
_.(GM)_
distance
1)
on
980.625
978,037.85
90°).
be
the
to
in
Consider
gravity
for
it
8.5):
from
SS
dk
(M)
location
the
can
8.4c),
respect
of
~
accounts
=
(R):
(Fig.
for
dg/dR
center
(R)
deviation
of increasing
_dg_
(@
distribution
~
theoretical
(Fig.
aR
value
the poles
of radius
8.6a).
g
components
be
radius
with
specific
of
the
would
air correction
oblate spheroid
values
average
(Fig.
Ag
KR
g,
elevation. That
Anomaly
from
the
of
mass
a
function
at
the
Hm.
function
0°)
Earth
at
changes
derivative
mGal
distance
average
_
main
observed
by
=
=
the
dg/dR
(@
the
for
The free
983,217.72
3)
Gravity
a
of three
a
an
equator
as
which
as
Earth: and
increasing
(Fig. 8.4c):
of
accounted
Assuming
to
first
(g)
such
changes
Gravity
mass
where:
due
point.
auion
tion,
Air
The
tion
For
the
ity
of
to
‘
Free
A R factors determining Three 8.5 FIGURE Observation an observation point: a) latitude gravity at Point » from sea-level datumto (&): b) distance (AR): c) observation point Earth’s mass distribution Topography (M), relative to the station ee includes material above as (M location level). @ is accounted as
the gravity from
to in sub- a 1967 sphere, 8.4a).
the equator compared poles. c) Variation (observed gravity), yielding by point imperfect poles
'212'686
pow = '6 then the of Geodesy: (Gal) (Fig.
22
at the (theoretical gravity), approximated Association observation Gal) an is the
= 0°) acceleration 983.000 Gal at is + 0.000023462sin‘d) Earth through
Equator (¢ 9, = 978,031.85 mGal gravitational o latitude station r latitude International of the (978,031.85 (degrees). the that axis an
nce in station's the at given the latitude equator point fact about
m/s? difference the equator. to about a value a by 0.005278895sin* the the the rotating
Isostasy 9.83 = —> the Formula. for value actual for gravity adopted + for gravity at gravity observation account and
and g & 983,000 mGal for 978,000 mGal at Gravity gravity the from of Formula, (1 g of the into equator
Gravity a m/s? 9.78 = ; ASE factors responsible from about Reference 1967 the value anomaly. Gravity value Gravity = 2, theoretical = theoretical = latitude = takes the at
Chapter8 = g g b => mGal main a) Three predicting by that tracting gravity Theoretical average The Reference where: g, 2. ¢ equation The out bulging
978,000 8.4
226 poles. b) Gravity increases equator to pole, according to
ge FIGURE