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，板块构造通过回收相对寒冷和坚硬的表层（即，地壳和岩石圈）到地幔的热内部，使其随时间冷却，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。板块构造在调节地球气候系统中起着重要作用。板块构造也雕刻了最重要的地表地形特征，如海洋盆地、洋中脊系统和主要的山脉带。板块构造决定了变形主要发生在板块边界（即，不同板块交汇处）通过地震和火山活动作为副产品。然而，尽管经过几十年的研究，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。该项目的关键方面是制定最先进的物理和动力学模型，将地震，地形和重力异常引起的观测变形纳入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。通过NSF支持的CIG（地球动力学计算基础设施），将进一步开发用于模拟岩石圈和地幔粘弹性非线性变形的社区有限元代码。该项目旨在模拟地震变形，地形和重力异常的观测，以限制板块内部（即，夏威夷）和会聚板块边界（日本海沟或俯冲带）的设置。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载荷引起的岩石圈变形对这两种不同构造背景下的低温塑性流动定律和摩擦系数有什么限制？第二，日本海沟的岩石圈流变学与夏威夷相比如何？考虑到日本海槽位于太平洋板块运动沿着夏威夷下游，从夏威夷到日本海槽岩石圈流变性是否演化以及如何演化？第三，日本海沟和夏威夷观测所约束的低温塑性流动定律与包括最近实验在内的实验室研究所导出的定律相比如何？为了回答这些问题，本项目将开展以下具体工作：1）根据地震资料估算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，并汇编其他观测资料，包括夏威夷附近和日本海沟的岩石圈偏转和外隆以及自由空间重力; 2）建立了日本海沟和夏威夷的载荷模型，计算了不同低温塑性流动规律和摩擦系数下岩石圈应变率、地形和重力的观测值，并将其与观察结果进行比较，以限制流变学;（3）检验了近年来的低温塑性流动规律，考察了岩石圈激活能和不同热结构对岩石圈载荷变形的影响，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.