Global azimuthal anisotropy in the transition zone

Area of Science:

• Geophysics
• Seismology
• Earth Science

Background:

• The Earth's mantle transition zone (400-660 km depth) plays a crucial role in mantle dynamics and chemical cycling.
• Understanding the physical properties, such as seismic anisotropy, is key to constraining models of this region.
• Azimuthal anisotropy, directional variations in seismic wave speeds, provides insights into preferred mineral orientations or textural fabrics.

Purpose of the Study:

• To investigate the presence and characteristics of azimuthal anisotropy within the Earth's mantle transition zone.
• To utilize surface wave dispersion data to probe seismic velocity structures at these depths.
• To provide new constraints on the mineralogy and dynamics of the transition zone based on observed anisotropy.

Main Methods:

• Analysis of surface wave dispersion measurements, specifically focusing on Love wave overtones.
• Application of Backus-Gilbert inversion techniques to anisotropic phase velocity maps.
• Ensuring resolution kernels are primarily sensitive to the transition zone (400-660 km depth).

Main Results:

• Evidence for significant azimuthal anisotropy was detected in the transition zone.
• A robust, long-wavelength azimuthally anisotropic velocity structure was identified.
• The inversion successfully mapped these anisotropic features within the target depth range.

Conclusions:

• The observed azimuthal anisotropy in the transition zone has important implications for understanding its composition and deformation.
• Potential sources of this anisotropy include aligned minerals, tilted laminated structures, or fluid inclusions.
• These findings offer new constraints for geodynamic and mineral physics models of the mantle transition zone.