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Seismic Velocity and Density Jumps Across the 410- and 660-Kilometer Discontinuities
1Institute 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.
Science (New York, N.Y.)
|September 8, 1999
Summary
Seismic wave analysis reveals new constraints on upper mantle discontinuities. The 660-kilometer discontinuity shows a smaller density jump than previously modeled, impacting mantle convection studies.
Area of Science:
- Geophysics
- Seismology
- Earth Science
Background:
- The 410-kilometer and 660-kilometer discontinuities are key interfaces in the Earth's upper mantle.
- Understanding seismic velocity and density changes at these depths is crucial for mantle dynamics.
Purpose of the Study:
- To determine the average seismic velocity and density jumps across the 410- and 660-kilometer discontinuities.
- To compare these values with existing models like the Preliminary Reference Earth Model (PREM) and pyrolite mantle models.
Main Methods:
- Modeling the range dependence of long-period seismic wave arrivals.
- Analyzing seismic wave reflections off the 410-km and 660-km discontinuities.
Main Results:
- The Preliminary Reference Earth Model (PREM) fits the 410-km discontinuity but not the 660-km discontinuity.
- Pyrolite mantle models align with the 410-km discontinuity but overpredict 660-km reflections.
- The density jump at the 660-km discontinuity is estimated to be 4–6%, lower than PREM's 9.3%.
Conclusions:
- The density jump at the 660-km discontinuity is significantly less than commonly used in mantle convection models.
- Revised seismic velocity and density data refine our understanding of upper mantle structure and dynamics.
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