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Simulation of the Planetary Interior Differentiation Processes in the Laboratory
Published on: November 15, 2013
Variable azimuthal anisotropy in Earth's lowermost mantle
Edward J Garnero1, Valérie Maupin, Thorne Lay
1Department of Geological Sciences, Arizona State University, Tempe, AZ 85287-1404, USA. garnero@asu.edu
Science (New York, N.Y.)
|October 9, 2004
Summary
Seismic wave polarity reversals at Earth's core-mantle boundary suggest deep mantle anisotropy. These findings point to mineral alignment in the D'' layer, potentially driven by mantle convection.
Area of Science:
- Geophysics
- Seismology
- Mineral Physics
Background:
- The D'' layer, Earth's lowermost mantle, exhibits complex seismic properties.
- Shear wave splitting and polarity reversals are key indicators of seismic anisotropy.
Purpose of the Study:
- Investigate the cause of persistent shear wave polarity reversals observed in the D'' layer.
- Determine the degree and pattern of azimuthal anisotropy at the base of the mantle.
Main Methods:
- Full waveform modeling of split shear waves for seismic paths beneath the Caribbean.
- Analysis of seismic wave behavior, specifically vertically and horizontally polarized shear waves.
Main Results:
- Observed shear wave polarity reversals correlate with the arrival of horizontally polarized shear waves.
- Azimuthal anisotropy at the base of the mantle is required to explain the split shear waves.
- Models consistent with data show transverse isotropy with tilted hexagonal symmetry axes (up to 20 degrees).
Conclusions:
- The observed seismic phenomena indicate laterally variable mineral alignment (crystallographic or shape-preferred orientation) within the D'' layer.
- Small-scale mantle convection cells above the D'' layer likely induce these variations, influencing mineral orientation.
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