Geodetic reference systems for crustal motion studies |
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| Authors: | RS Mather&#x; C Rizos R Coleman EG Masters |
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| Institution: | R.S. Mather?, C. Rizos, R. Coleman,E.G. Masters |
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| Abstract: | The behaviour of geodetic reference systems as a function of time cannot be ignored in determinations of position for secular geodynamic modelling. While non-specialist users are likely to appreciate the uncertainty surrounding the concept of a “fixed” point in regional surveys for crustal motion, its extension to global surveys based on techniques in dynamic geodesy is not widely understood. Such solutions are related to the natural coordinate system defined by the instantaneous geocentre (earth's centre of mass) and the instantaneous rotation axis whose location in earth space cannot be expected to be time invariant.The effect of such movements of the natural system of reference on the coordinates of points at the earth's surface is computed for a plausible model of the former. The resulting changes in solutions for three-dimensional position from dynamic considerations are discussed. It is shown that for the model adopted, the earth-space variations of the natural reference system with time produce coordinate changes with magnitudes not dissimilar to those resulting from reasonable variations in the earth's figure, though with different wavelengths, when computed from three-dimensional considerations alone.The resulting displacements, along with an accepted model for plate motions, are used to study changes in the shape of the level surfaces of the earth's gravity field with time. It is shown that plausible models for the deformation of the earth's figure produce significant changes in the geopotential and the shape of the geoid. However, the transfer of mass implied in extreme models of plate motion produce no significant changes in the datum level surface for crustal motion studies over periods as long as 102 yr. |
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