南方科技大学
据悉，地球地幔的可变黏度对地幔对流和板块构造具有重要的控制作用，但如何严格地约束其基本参数仍然是一个挑战。反演方法还不够成熟，无法处理严重的粘度梯度和非线性(由位错蠕变和塑性破坏引起)，同时解决大逆冲和整体板块弯曲。
本研究利用全球板块运动作为约束条件，将可扩展的非线性Stokes解算器与基于伴随的贝叶斯方法相结合来克服这些挑战，该解算器解决了关键的构造特征。假设板块冷却、大陆岩石圈、板块和大范围下地幔结构的厚度变化以及上地幔整体粒度的恒定，则上地幔应力非线性指数为2.43±0.25 (平均值±SD)，与全球板块运动吻合较好。
在俯冲过程中，板块需要相对较低的屈服应力(151±19MPa)才能弯曲，并传递板块拉力，从而产生不对称俯冲。在不同的俯冲带之间，巨型逆冲断层(板块界面)的恢复长期强度有所不同，南美洲的强度较大，瓦努阿图和中美洲的强度较低，这对驱动巨型逆冲断层的应力具有重要意义。
附：英文原文
Title: Constraining Earth’s nonlinear mantle viscosity using plate-boundary resolving global inversions
Author: Hu, Jiashun, Rudi, Johann, Gurnis, Michael, Stadler, Georg
Issue&Volume: 2024-7-5
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.
DOI: 10.1073/pnas.2318706121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2318706121