ON THE POSSIBILITY OF GLOBAL AND REGIONAL INVERSION OF EXOGENIC DEFORMATIONS FOR MECHANICAL-PROPERTIES OF THE EARTHS INTERIOR

Seismic tomography has proven to be a powerful method for studying thr ee-dimensional properties of the faith's interior. Using seismic waves , however, limits the principally accessible period range to periods l ess than 1 h. Furthermore, density is not among the parameters that ca n be derived unambiguously from seismic tomography. The redistribution of mass on the Earth's surface due to a wide variety of meteorologica l processes provides a continuous source of deformations of the Earth, and these deformations depend on the mechanical properties of the Ear th. The increasing capabilities of space-geodetic methods and the avai lability of global meteorological data open up new perspectives for ut ilizing these broadband exogenic deformations to study the mechanical properties of the Earth in a period range not accessible by seismic te chniques. To develop an inversion method based on exogenic deformation s, several problems have to be solved: (1) the direct modelling of exo genic deformations has to be formulated for laterally heterogeneous Ea rth models;(2) the requirements for geodetic networks to continuously monitor exogenic deformations have to be specified in terms of spatial resolution; (3) a time-domain inversion method has to be established; and (4) for regional studies, a working model of the far-field contri bution has to be set up. In the present paper, the theoretical problem s involved in (1) are discussed. The effect of lateral heterogeneities on exogenic deformations due to meteorological loading are discussed, and found to be of an order sufficient to allow for an inversion. The explicit expressions relating the Green's functions for surface loadi ng on a laterally heterogeneous Earth to the mechanical properties of the model are given. These expressions are based on an expansion in sp herical harmonics. Due to computational limits, it is concluded, that this approach will be feasible for global inversions with a resolution considerably higher than present-day global seismic tomography. For r egional inversions, however, another approach will be required, using the global spherical harmonic solution to model the far-field contribu tion.