Geoscience Reference
In-Depth Information
6km
4km
3km
2km
5km
H
H'
.
D=100 km
2.67 2.62 2.57 2.59 2.52 2.67 2.76
level of compensation
Fig. 3.9. Pratt-Hayford isostasy model
which expresses the condition of equal mass. It may be assumed that
0
=2
.
67 g cm
−
3
.
(3-49)
According to (3-48), the actual density
is slightly smaller than this normal
value
0
. Consequently, there is a mass deficiency which, according to (3-48),
is given by
h
D
+
H
0
.
∆
=
0
−
=
(3-50)
In the oceans, the condition of equal mass is expressed as
(
D
H
)
+
H
w
=
D
0
,
−
(3-51)
where
w
=1
.
027 g cm
−
3
(3-52)
is the density and
H
the depth of the ocean. Hence, there is a mass surplus
of a suboceanic column given by
H
−
0
=
(
0
−
w
)
.
(3-53)
H
D
−
As a matter of fact, this model of compensation is idealized and schematic.
It can be only approximately fulfilled in nature. Values of the depth of com-
pensation around
D
= 100 km
(3-54)
