certainly exhibit lateral variations for there is abundant geophysical evidence for
lateral variations in a variety of physical properties of the Earth. Clearly, the
ultimate function will be complex but nevertheless it is important to attempt to
define it for once it, or part of it, is mapped it becomes possible to make
predictions about the forces responsible for some of the other deformations of
the Earth. It should become possible, for example, to draw conclusions about
mantle convection and the driving forces of plate tectonics.
Conclusions
From these few examples, I hope to have illustrated that geodesy is very much
an integral part of the Earth Sciences. In so doing I may be accused of taking a
narrow view in that I am ignoring much of the traditional areas of geodesy
concerned with determining the "shape of the Earth". This would, however, be
incorrect for these 'traditional' areas form the very underpinning of the Earth
Science applications. One example, obvious in the context of this fifty year
anniversary, is the important work carried out on evaluating geodetic networks
at the Geodesy Faculty of Delft. This now provides a very sound basis for
evaluating time dependencies of these networks produced by the Earth itself and
not by the whims of geodetic measurements.
Perhaps I could also stand accused of attributing too much to the discipline of
geodesy, of including too many other areas of the Earth Sciences under the
umbrella of geodetic science, and of insisting that geophysical causes are as much
part of the subject as are the effects measured by geodetic techniques. If I were
so accused I suspect that I stand in good company for past geodesists did not
have such reservations. Neither do seismologists confine themselves to describing
or analyzing their data. They also seek causes. Geodetic science has entered into
its most exciting era now and it would be a shame to miss out on the fun.
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Figure 1: Two recorders of Earth deformation.
(a) A conglomerate from the Jack Hills area of Western Australia containing a record
of Earth deformation spanning 4.2 billion years.
(b) A radio-telescope used for long baseline radio interferometry observations of Earth
deformation on time scales of hours to years.
Figure 2: The relation between force and deformation for the Earth. In the first example the force
is known and the response function of the Earth is deduced from the observation. Once
this function is determined unknown forces can be quantified from observations of
deformation (the second example).
Figure 3: Typical observations of sea-level positions, relative to the crust, from different locations
around the world (note the different height scales used in all examples).