Large Scale Aspherical Earth Structure

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The availability of a large quantity of long-period digital seismic data has played a major role in recent advances in our understanding of the large-scale aspherical structure of the Earth. Many new models exist which have been designed to fit these data. They succeed to various degrees but it is indisputable that much of the signal in the data remains to be explained. One reason for this is that approximate theoretical formulations have been used to intepret the data. In this proposal, we describe techniques of data analysis which can avoid most approximations and we illustrate how well some approximate techniques are capable of performing. The application of these techniques to a large dataset will lead to many integral constraints on aspherical structure which we call structure coefficients. These structure coefficients can also be used to compute three-dimensional Green's functions for accurate studies of long-period source mechanisms.