An inversion for radial viscosity structure using seismic tomography

Using a uniform velocity/density scaling, we have inverted the seismically inferred 3-dimensional structure of the whole manfie for the radial viscosity structure which best fits the geoid. We are able to obtain 60-72% variance reductions for three different S-wave tomographic models. The resulting viscosity structures are remarkably similar, showing a high viscosity lid, a low viscosity zone in the transition region and a high viscosity lower manfie. A resolution analysis indcates that the viscosity structure in the upper manfie is well resolved by the data, however the resolution in the lower manfie is poorer. Our models axe in general agreement with previous studies except that our inversions prefer a low viscosity layer at 400-670 km as opposed to 100-400 kin.

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