Insights on Upper Mantle Melting, Rheology, and Anelastic Behavior From Seismic Shear Wave Tomography
Laura Cobden1, Jeannot Trampert1, Andreas Fichtner1,2
1Department of Earth Sciences Utrecht University Utrecht Netherlands.
Geochemistry, Geophysics, Geosystems : G(3)
|April 23, 2019
Summary
Seismic tomography reveals Earth's mantle properties by analyzing S-wave speeds. This study links wave speeds to thermochemical models, considering factors like temperature, composition, and water content.
Area of Science:
- Geophysics
- Seismology
- Earth Science
Background:
- Seismic tomography images Earth's interior wave speed structure.
- Interpreting wave speeds in terms of physical parameters is challenging due to trade-offs.
- Mapping seismic structures as relative perturbations complicates absolute value interpretation.
Purpose of the Study:
- To quantify the constraints on thermochemical and dynamic mantle properties using absolute S-wave speeds.
- To investigate the role of intrinsic anelasticity and its frequency dependence.
- To compare seismic tomography models with extensive thermochemical models.
Main Methods:
- Utilized a full waveform tomography model of Europe.
- Compared wave speed distributions with 4 million thermochemical models.
- Incorporated thermodynamic modeling for seismic properties, including water, melt, and intrinsic anelasticity.
- Filtered thermochemical models based on the anticorrelation between S-wave speed and attenuation.
Main Results:
- Demonstrated that absolute S-wave speeds can constrain thermochemical and dynamic properties.
- Quantified the frequency dependence of anelasticity (α), finding it varies with temperature/rheology (α ≈ 0.1 in cold mantle, α ≈ 0.3 in asthenosphere).
- Identified that the slowest mantle regions require specific compositions or velocity-weakening mechanisms like partial melting or water.
Conclusions:
- Absolute S-wave speed tomography provides valuable constraints on mantle properties.
- The frequency dependence of anelasticity is a key factor in interpreting seismic data.
- Understanding mantle composition and physical processes is enhanced by integrating seismic and thermodynamic models.
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