Chris,

I've written quite a few papers on body waves turning in the mantle, and grazing the upper mantle discontinuities and the core-mantle boundary, so I don't expect that Lowell's thesis would change my mind. His expertise is prediction, not mantle structure nor wave propagation.

I'm confident that there are not distinct peaks in the amplitudes of seismic waves at the distances of the rings, particularly if surface waves are included and the longer periods most likely to trigger earthquakes considered.

John