title: Seismic Velocity and Density Jumps Across the 410- and 660-Kilometer Discontinuities.
abstract: The average seismic velocity and density jumps across the 410- and 660-kilometer discontinuities in the upper mantle were determined by modeling the observed range dependence in long-period seismic wave arrivals that reflect off of these interfaces. The preliminary reference Earth model (PREM) is within the computed 95 percent confidence ellipse for the 410-km discontinuity but outside the allowed jumps across the 660-kilometer discontinuity. Current pyrolite mantle models appear consistent with the constraints for the 410-kilometer discontinuity but overpredict amplitudes for the 660-kilometer reflections. The density jump across the 660-kilometer discontinuity is between 4 and 6 percent, below the PREM value of 9.3 percent commonly used in mantle convection calculations.
authors.affiliation: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0225, USA. Lawrence Livermore National Laboratory, Post Office Box 808, L-206, Livermore, CA 94551, USA.
authors.initials: PM
authors.lastname: Shearer
authors.initials: MP
authors.lastname: Flanagan