Regional Studies of Anisotropy Beneath the Pacific Ocean

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Several studies in recent years have confirmed that both the crust and upper mantle beneath oceanic regions are anisotropic in their elastic properties. We propose to study the nature of that anisotropy by comparisons of observed waveforms recorded at regional and near distances with those calculated for models of generalized anisotropy which can include up to 13 eleastic constants and which can vary from layer to layer in magnitude and direction. By restricting our observations to waves which have traveled short distances we will minimize any effects of lateral heterogeneity of velocity structure on wave forms, increase the likelihood that the orientation and magnitude of anisotropy is uniform along that path, and, if paths of different distances are available, may be able to separate the effects of varying anisotropic structure in the upper crust, lower crust, and upper mantle. In addition, since short paths are used, it will be possible to use small events which are numerous in many parts of the Pacific.