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Robust normal mode constraints on inner-core anisotropy from model space search.
Caroline Beghein1, Jeannot Trampert
1Faculty of Earth Sciences, Utrecht University, Post Office Box 80021, 3508 TA Utrecht, Netherlands. beghein@geo.uu.nl
Science (New York, N.Y.)
|January 25, 2003
Summary
Seismic wave anisotropy in Earth's inner core reveals distinct P-wave and S-wave patterns. These findings suggest a changing structure and potential new iron phase at the inner core's center.
Area of Science:
- Geophysics
- Seismology
- Earth Science
Background:
- Earth's inner core exhibits complex seismic properties.
- Understanding inner core anisotropy is crucial for geodynamic models.
Purpose of the Study:
- To investigate the seismic anisotropy of Earth's inner core.
- To characterize the behavior of P-wave and S-wave anisotropy with depth.
Main Methods:
- Applied a novel technique for searching full model space to seismic normal mode measurements.
- Analyzed anomalously split normal modes to determine anisotropy patterns.
Main Results:
- Observed a robust pattern of P-wave and S-wave anisotropy in the inner core.
- P-wave anisotropy parameter changes sign at approximately 400 km radius.
- S-wave anisotropy is minimal in the upper inner core, becoming negative at greater depths.
Conclusions:
- Results align with travel-time anomalies at large epicentral distances (150-180 degrees).
- Models suggest progressively tilted hexagonal close-packed iron in the upper inner core.
- A different iron phase may exist in the inner core's center.
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