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，板块构造控制着地球的热演化，将相对寒冷和坚硬的表层（即地壳和岩石圈）再循环到地幔的热内部，使其随着时间的推移而冷却，从而决定了地球磁场的产生。板块构造是地球独有的特征，在我们太阳系的其他类地行星上并不存在。人们认为板块构造在调节地球气候系统中起着重要作用。板块构造还雕刻了最重要的表面地形特征，如海洋盆地、洋中脊系统和主要山带。板块构造学表明，变形主要发生在板块边界（即不同板块相交的地方），通过地震和火山活动作为副产品。然而，尽管经过了几十年的研究，板块构造的成因仍然很大程度上是未知的。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建立最先进的物理和动力学模型，将观测到的地震、地形和重力异常引起的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。进一步开发社区有限元代码，用于模拟岩石圈和地幔的粘弹性、非线性变形，将通过美国国家科学基金会支持的CIG（地球动力学计算基础设施）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结果，以约束板块内部（即夏威夷）和板块收敛边界（日本海沟或俯冲带）环境下的岩石圈流变。该项目解决了以下三个地球物理问题。首先，日本海沟和夏威夷岩石圈载荷引起的变形观测对这两种不同构造环境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学与夏威夷的比较如何？考虑到日本海沟沿太平洋板块运动在夏威夷的下游，岩石圈流变学是否从夏威夷向日本海沟演化，又是如何演化的？第三，日本海沟和夏威夷观测约束下的低温塑性流动规律与包括近期实验在内的实验室研究结果如何比较？为了回答这些问题，本项目将开展以下具体工作：1)根据地震信息估算夏威夷地区和日本海沟的地震应变率，量化地震应变率的不确定性，并编制夏威夷附近和日本海沟附近岩石圈挠度、外隆起和自由空气重力等观测资料；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岩石圈应变率、地形和重力的观测值，并与观测值进行对比，对流变性进行约束；3)利用近期实验验证低温塑性流动规律，考察活化能和不同岩石圈热结构对载荷诱导岩石圈变形的影响，重新标定岩石圈屈服强度。该奖项反映了美国国家科学基金会的法定使命，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.