Seismic Velocity and Density Jumps Across the 410- and 660-Kilometer Discontinuities
Peter M. Shearer,
1*
Megan P. Flanagan
2
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.
1 Institute of Geophysics and Planetary
Physics, Scripps Institution of Oceanography, University of California,
San Diego, La Jolla, CA 92093-0225, USA.
2 Lawrence
Livermore National Laboratory, Post Office Box 808, L-206, Livermore,
CA 94551, USA.
*
To whom correspondence should be addressed.
