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Constrained reference mantle model

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Caltech Authors


A dataset of updated normal mode eigenperiods is used to develop a new average upper mantle model. The starting model takes account of recent body wave and surface wave models and of constraints derived from different petrological models. Different parameterizations with or without anisotropy down to different depths are checked. Anisotropy seems to be required at least down to 200 km and preferably down to 400 km but with a smaller amplitude than in the preliminary reference Earth model (PREM). The new models provide velocity gradients down to 400 km in good agreement with finite strain trajectories. The S-wave velocity jump at 400 km is smaller than previously found from regional studies. If the S-wave and P-wave velocity jumps at the 400-km discontinuity are considered simultaneously, this discontinuity cannot be explained by an upper mantle composed mainly of olivine.

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