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2.7.4 Physical properties of the Earth
A set of conventional constants, based mainly on data
from artificial satellites and radar observations of the Moon and the planets,
was adopted by the International Union of Geodesy and Geophysics in 1979. While
adopted as conventional values, they also represent the best observational data
very closely. In the following table, values given under ‘Whole
Earth’ are IUGG primary constants (p) or are derived from
them.
The Earth: mechanical properties
|
|
Property |
Whole Earth |
Core |
|
|
|
|
|
|
p |
Equatorial radius, a . . . . . . . . . .
. . |
6378.137 km |
3488 km |
|
|
Polar radius, c . . . . . . . . . . . . .
. |
6356.752 km |
3479 km |
|
|
Polar flattening, f = (a −
c)/a . . . . . . . . . |
1/298.2572 |
1/390 |
|
|
Mean radius
(a2c)1/3 . . . . . . . . . . .
. |
6371.00 km |
3485 km |
|
|
Mass M . . . . . . . . . . . . . . .
. |
5.976 × 1024 kg |
1.88 × 1024 kg |
|
|
Mean density . . . . . . . . . . . . . . |
5518 kg m −3 |
10 720 kg m−3 |
|
|
Moments of inertia in terms of
Ma2 |
|
|
|
|
Polar
C/Ma2 . . . . . . . . . . . . . |
0.3306 |
0.380 |
|
|
Equatorial
A/Ma2 . . . . . . . . . . . . |
0.3295 |
|
|
p |
GM . . . . . . . . . . . . . . . .
. |
398 600.5 × 109 m3
s−2 |
|
|
p |
J2 = (C −
A)/Ma2 . |
1.082 63 × 10−3 |
|
|
|
Dynamical ellipticity (C
−A)/C . . . . . . . . |
3.275 × 10−3 |
|
|
|
Angular velocity . . . . . . . . . . . .
. |
7.292 1152 × 10−5
rad/s |
|
|
|
Surface area . . . . . . . . . . . . . . |
5.101 × 1014 m2 |
1.52 × 1014 m2 |
|
|
Volume . . . . . . . . . . . . . . . . |
1.083 × 10 21 m 3 |
0.176 × 10 21 m3 |
|
|
Quadrant of meridian . . . . . . . . . .
. |
10 002.002 km |
5640 km |
|
|
|
|
|
The Earth: variation of properties with depth
It is not possible to construct a unique model of the variation of
mechanical properties within the Earth, but the values in the Table are
representative.
|
Zone |
|
|
Elastic wave
velocity |
|
|
Rigidity
modulus |
|
1011 N m−2 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| |
0 |
2 400 |
4.30 |
2.30 |
— |
— |
0 |
9.82 |
| |
60 |
3 365 |
8.04 |
4.45 |
1.30 |
0.65 |
0.018 |
9.85 |
| |
150 |
3 380 |
8.05 |
4.40 |
1.32 |
0.65 |
0.048 |
9.88 |
| |
350 |
3 518 |
8.80 |
4.76 |
1.77 |
0.79 |
0.117 |
9.95 |
|
Mantle |
500 |
3 845 |
9.68 |
5.24 |
2.19 |
1.06 |
0.172 |
9.99 |
| |
1000 |
4 595 |
11.47 |
6.42 |
3.52 |
1.89 |
0.388 |
9.97 |
| |
1500 |
4 870 |
12.19 |
6.70 |
4.33 |
2.18 |
0.623 |
9.92 |
| |
2000 |
5 090 |
12.81 |
6.95 |
5.08 |
2.46 |
0.870 |
9.99 |
| |
|
2885 |
 |
|
5 745 |
13.37 |
7.21 |
6.66 |
2.90 |
 |
1.356 |
|
10.70 |
| |
9.860 |
8.08 |
0 |
6.43 |
0 |
| |
3500 |
10 930 |
8.88 |
0 |
8.35 |
0 |
1.936 |
9.75 |
|
Core |
4000 |
11 310 |
9.52 |
0 |
10.45 |
0 |
2.467 |
7.88 |
|
4500 |
11 820 |
9.98 |
0 |
11.70 |
0 |
2.882 |
6.28 |
| |
5000 |
12 120 |
10.24 |
0 |
12.66 |
0 |
3.214 |
4.92 |
| |
| 5155 |
|
|
12 170 |
10.27 |
0 |
12.84 |
0 |
|
3.302 |
|
4.50 |
| |
13 050 |
10.96 |
3.50 |
13.54 |
1.60 |
|
Inner |
|
|
|
|
|
|
|
|
|
core |
6371 |
13 340 |
11.29 |
3.63 |
14.66 |
1.76 |
3.67 |
0 |
|
|
|
|
|
|
|
|
|
|
P—Compressional wave; S—Shear
wave
The Earth: other physical constants
|
Land: |
area . . . . . . . . . . . . . |
1.49 × 1014 m2 (29.2 per cent of
Earth’s surface) |
|
|
mean height . . . . . . . . . . |
840 m |
|
|
greatest height . . . . . . . . . |
8840 m |
| |
|
|
|
Oceans: |
area . . . . . . . . . . . . . |
3.61 × 1014 m2 (70.8 per cent of
Earth's surface) |
|
|
volume . . . . . . . . . . . . |
1.37 × 1018 m3 |
|
|
mass . . . . . . . . . . . . |
1.42 × 1021 kg |
|
|
mean depth . . . . . . . . . . |
3800 m |
|
|
greatest depth . . . . . . . . . |
10 550 m |
|
Atmosphere: |
mass . . . . . . . . . . . . |
5.27 × 1018 kg (10−6 of
Earth’s mass) |
Heat flow from the interior of the Earth
Heat flows out from the interior of the Earth at the rate of 0.059
Wm−2 through the continents and 0.10 Wm−2
through the oceans. The total rate of heat loss from the whole surface of the
Earth is about 4.2 × 1013 W.
References
K. Bullen and B. A. Bolt (1985) An Introduction to the Theory of
Seismology, Cambridge University Press, Cambridge.
Geodetic
Reference System (1980), IUGG.
J. G. Slater, C. Jaupart, and D. Galson
(1970) Rev. Geophys. Space Phys. 18, 269–311. W. Torge
(1991) Geodesy, 2nd edn, de Gruyter, Berlin, New York.
Sir Alan Cook
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