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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 = (ac)/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 = (CA)/Ma2 .

  1.082 63 × 10−3

 

 

Dynamical ellipticity (CA)/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

Depth

km

Density

kg m−3

Elastic wave
velocity

Bulk
modulus

1011 N m−2

Rigidity
modulus

1011 N m−2

Pressure

1011 N m−2

g

m s−2

P

km s−1

S

km s−1

 

           

 

 

 

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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