Geoscience Reference
In-Depth Information
2km
H
H'
T=30km
density 2.67
t'
8.9 km
t
density 3.27
Fig. 3.10. Airy-Heiskanen isostasy model
for the numerical values assumed.
Again, spherical corrections must be applied to these formulas for higher
accuracy, and the formulations in terms of equal mass and equal pressure
lead to slightly different results.
The normal thickness of the earth's crust is denoted by
T
(Fig. 3.10);
values of around
T
= 30 km
(3-62)
are assumed. The crustal thickness under mountains is then
T
+
H
+
t
(3-63)
and under the oceans it is
H
−
t
.
T
−
(3-64)
Vening Meinesz regional system
Both systems just discussed are highly idealized in that they assume the
compensation to be strictly local; that is, they assume that compensation
takes place along vertical columns. This presupposes free mobility of the
masses to a degree that is obviously unrealistic in this strict form.
For this reason, Vening Meinesz modified the Airy floating theory in 1931,
introducing regional instead of local compensation. The principal difference
between these two kinds of compensation is illustrated by Fig. 3.11. In Vening
