Published July 9, 2024
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Journal Article
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Constraining Earth's nonlinear mantle viscosity using plate-boundary resolving global inversions
Abstract
Variable viscosity in Earth’s mantle exerts a fundamental control on mantle convection and plate tectonics, yet rigorously constraining the underlying parameters has remained a challenge. Inverse methods have not been sufficiently robust to handle the severe viscosity gradients and nonlinearities (arising from dislocation creep and plastic failure) while simultaneously resolving the megathrust and bending slabs globally. Using global plate motions as constraints, we overcome these challenges by combining a scalable nonlinear Stokes solver that resolves the key tectonic features with an adjoint-based Bayesian approach. Assuming plate cooling, variations in the thickness of continental lithosphere, slabs, and broad scale lower mantle structure as well as a constant grain size through the bulk of the upper mantle, a good fit to global plate motions is found with a nonlinear upper mantle stress exponent of 2.43 ± 0.25 (mean ± SD). A relatively low yield stress of 151 ± 19 MPa is required for slabs to bend during subduction and transmit a slab pull that generates asymmetrical subduction. The recovered long-term strength of megathrusts (plate interfaces) varies between different subduction zones, with South America having a larger strength and Vanuatu and Central America having lower values with important implications for the stresses driving megathrust earthquakes.
Copyright and License
© 2024 the Author(s). Published by PNAS. This article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).
Acknowledgement
Computations were carried out on the NSF-supported Stampede-2 and Frontera supercomputers at the Texas Advanced Computer Center under allocations TG-EAR160027, TG-DPP130002, and FTA-SUB-CalTech, and Anvil at Purdue University (Rosen Center for Advanced Computing) under allocations EAR-160027. J.H. was further supported by the National Key R&D Program of China through award 2023YFF0806300 and National Natural Science Foundation of China through award 92155307.
Contributions
J.H. and M.G. designed research; J.H. performed research; J.R., M.G., and G.S. contributed new reagents/analytic tools; J.H. and M.G. analyzed data; and J.H., J.R., M.G., and G.S. wrote the paper.
Data Availability
Model data and postprocessing scripts have been deposited to Zenodo (https://doi.org/10.5281/zenodo.11697180) (70). All other data are included in the article and/or SI Appendix.
Conflict of Interest
The authors declare no competing interest.
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Additional details
- ISSN
- 1091-6490
- National Science Foundation
- TG-EAR160027
- Texas Advanced Computing Center
- TG-DPP130002
- Texas Advanced Computing Center
- FTA-SUB-CalTech
- National Science Foundation
- EAR-160027
- Ministry of Science and Technology of the People's Republic of China
- 2023YFF0806300
- National Natural Science Foundation of China
- 92155307
- Caltech groups
- Division of Geological and Planetary Sciences, Seismological Laboratory