The development of cross-spectral techniques for investigating the relation between gravity and topography has led to the representation of isostatic processes in terms of mathematical filters, or admittance functions. These filters can easily be constructed by application of Greens equivalent layer theorem. The rheology of the lithosphere principally controls the process by which isostatic compensation is achieved. As examples, admittance functions representing the isostatic process defined by elastic and visco-elastic rheologies are developed. By using admittance functions, the calculation of the free-air gravity anomaly for complicated topography, isostatic schemes, or rheology becomes computationalIy more efficient and simple compared to the more conventional line-integral methods.
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