Constraining Frictional and Low-Temperature Plastic Rheology of Oceanic Lithosphere by Modeling Observations of Load-Induced Deformation from the Hawaiian Islands to Japan Trench

板块构造可以说是固体地球最重要的物理过程。从基础科学的角度来看，板块构造通过将相对冷硬的表层(即地壳和岩石圈)循环到地幔内部较热的地方，使其随时间冷却而控制地球的热演化，这决定了地球磁场的产生。板块构造是地球的一个独特特征，在我们太阳系的其他类地行星上不存在。板块构造被认为在调节地球气候系统中发挥重要作用。板块构造还雕刻了最重要的地表地貌特征，如大洋盆地、大洋中脊体系和主要山带。板块构造规定，变形主要发生在板块边界(即不同板块交界处)，伴随着火山活动。然而，尽管进行了数十年的研究，但板块构造的原因在很大程度上仍然未知。该项目旨在揭示板块构造的物理机制。该项目的关键是建立最先进的物理和动力学模型，将地震、地形和重力异常造成的观测变形整合到我们对板块构造生成的理解中。该项目将支持一名博士生，并包括重要的国际合作。进一步开发一个用于模拟岩石圈和地幔的粘弹性、非线性变形的社区有限元程序，将通过NSF支持的地球动力学计算基础设施(CIG)提供给社区。该项目旨在模拟地震变形、地形和重力异常的观测，以约束板块内部(即夏威夷)和收敛的板块边界(日本海沟或俯冲带)的岩石圈流变学。该项目涉及以下三个地球物理问题。首先，在日本海沟和夏威夷观测到的负载引起的岩石圈变形对这两个不同构造背景下的低温塑性流动规律和摩擦系数有什么约束？第二，日本海沟的岩石圈流变性与夏威夷海沟的岩石圈流变学相比如何？考虑到日本海沟位于夏威夷的下游，沿着太平洋板块运动，岩石圈的流变性是否从夏威夷演化到日本海沟以及如何演化？第三，在日本海沟和夏威夷观测到的低温塑性流动规律与包括最近的实验在内的实验室研究得出的结果相比如何？为了回答这些问题，本项目将执行以下具体任务：1)根据地震信息估计夏威夷地区和日本海沟的地震应变率，量化它们的不确定性，并汇编其他观测数据，包括夏威夷附近和日本海沟的岩石圈偏转、外部隆起和自由空气重力；2)建立日本海沟和夏威夷的加载模型，计算不同低温塑性流动规律和摩擦系数下的岩石圈应变率、地形和重力观测值，并将它们与观测结果进行比较，以对流变性施加约束；3)测试最新实验的低温塑性流动规律，考察活化能和不同的岩石圈热结构对载荷引起的岩石圈变形的影响，并重新校准岩石圈屈服强度。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，认为值得支持。

Plate tectonics is arguably the most important physical process of the solid Earth. From the fundamental science point of view, plate tectonics controls the thermal evolution of the Earth by recycling the relatively cold and stiff surface layer (i.e., the crust and lithosphere) to the hot interiors of the Earth's mantle to cause its cooling down with time, which determines the generation of Earth's magnetic field. Plate tectonics is a unique feature to the Earth and does not exist for other terrestrial planets in our solar system. Plate tectonics is suggested to play an important role in regulating the Earth's climate system. Plate tectonics also carves the most important surface topographic features such as ocean basins, mid-ocean ridge systems, and major mountain belts. Plate tectonics dictates that deformation occurs primarily at plate boundaries (i.e., where different plates meet) through earthquakes with volcanism as by-products. However, the cause of plate tectonics remains largely unknown, despite decades of research. This project is aimed at uncovering the physical mechanism for plate tectonics. The key aspect of this project is to formulate state of art physical and dynamic models to integrate the observed deformation caused by earthquakes, topography and gravity anomalies into our understanding of plate tectonics generation. This project will support a PhD student and includes significant international collaboration. The further development a community finite element code for modeling viscoelastic, non-linear deformation of lithosphere and mantle, will be made available to the community through NSF-supported CIG (Computational Infrastructure for Geodynamics).This project seeks to model observations of earthquake deformation, topography and gravity anomalies to constrain lithospheric rheology in both plate interior (i.e., Hawaii) and convergent plate boundary (Japan trench or subduction zone) settings. The project addresses the following three geophysical questions. First, what constraints would the observations of load-induced lithospheric deformation at the Japan trench and Hawaii place on the low-temperature plasticity flow laws and coefficient of friction in these two different tectonic settings? Second, how does lithospheric rheology in the Japan trench compare with that at Hawaii? Considering that the Japan trench is downstream of Hawaii along the Pacific plate motion, does the lithospheric rheology evolve from Hawaii to Japan trench and how? Third, how do the low-temperature plasticity flow laws constrained by the observations at Japan trench and Hawaii compare with those derived from laboratory studies including recent experiments? To answer these questions, this project will carry out the following specific tasks: 1) Estimate seismic strain rate for the Hawaiian region and Japan trench from earthquake information, quantify their uncertainties, and compile other observations including lithospheric deflection near Hawaii and at Japan trench and outer rise and free-air gravity; 2) Formulate loading models for the Japan trench and Hawaii to compute the observables of lithospheric strain rate, topography and gravity for different low-temperature plasticity flow laws and coefficient of friction, and compare them with observations to place constraints on the rheology; 3) Test low-temperature plasticity flow laws from recent experiments, examine the effect of the activation energy and different lithospheric thermal structure on load-induced lithospheric deformation, and re-calibrate the lithospheric yield strength.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.