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. 361 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).

Digitale Tijdschriftenarchief Stichting De Hollandse Cirkel en Geo Informatie Nederland

Lustrumboek Snellius | 1990 | | pagina 384