Dynamic Linkages between the Transition Zone & Surface Plate Motions in 3D Models of Subduction

构造板块在地球表面的运动是由地幔内部的力引起的：扩张脊处的正浮力推动，俯冲带处的下沉板块(板块)拉动。在地球表面，这些力导致地震，两个板块相互滑动(板块边界)。下沉的板块所产生的力量有效地将构造板块拉到身后的能力，取决于板块在地幔内的变形方式，而地幔的变形又取决于板块的材料特性在变形过程中的变化。此外，与下沉板相关的总力取决于矿物晶体结构的变化(相变)，这会导致板内密度的变化。这些相变大部分发生在地球表面下410至660公里之间，这一区域被称为过渡带。最终，地幔内部下沉板块的变形表现在板块内发生的地震活动中，深至地球表面下660公里处，并可观察到地球表面板块运动的变化。这项研究的目的是确定，1)表层板块运动和板块内部的应力状态如何对板块过渡过程中的板块动力学做出反应并提供反馈；2)板块深部地震活动的起源是什么；3)板块的观测形状是否与俯冲板块和板块边界的固有性质有关，或者是板块随时间变化的反映。虽然这项研究的重点是地球内部的变形-S地幔，但这种变形与地球表面板块的运动耦合，可能引起破坏性地震和海啸。为了解决这些问题，将发展俯冲动力学的三维数值模型(模拟)。更具体地说，我们将对板块的矿物组成(地壳、残余方辉橄榄岩和地幔)、相变(包括所有主要矿物成分)和板块和地幔的流变性使用最佳的实验室和观测约束。我们将启用动态移动的板和板边界，这对于理解板坯变形和表面板运动之间的物理联系是必不可少的。这些模型消除了以前研究中使用的几个简化假设，使我们能够在板片变形与表面板块运动和板片地震活动之间建立联系。模型结果将与有关板块形状、板块特征和运动学的全球数据集以及关于板块内应力状态和整个俯冲岩石圈的地震不连续(在相变时发生)的区域地震观测结果进行比较。该项目的成果将对控制板块变形的物理过程及其拉动构造板块的能力提供更完整和现实的理解，并深入了解板块地震活动与更大范围的变形板块之间的关系。此外，这项研究将支持博士生的培训，为建模社区贡献软件，向本科生介绍科学研究，并为本科生教学中使用的材料做出贡献。

The motion of tectonic plates at the surface of the earth is caused by forces within the earth's mantle: the push of positive buoyancy at spreading ridges and the pull of sinking plates (slabs) at subduction zones. At the earth's surface these forces result in earthquakes where the two plates slide past one another (plate boundaries). The ability of the force from sinking slabs to effectively pull tectonic plates behind them depends on how the slab deforms within the earth's mantle, which in turn depends on how its material properties change as it deforms. In addition, the total force associated with the sinking slab depends on changes in the crystal structure of the minerals (phase changes), which lead to changes in density within the slab. Most of these phase changes occur between 410 and 660 km beneath the earth's surface, a region known as the transition zone. Ultimately, the deformation of the sinking slab inside the mantle is manifest in seismicity occurring within the slab to depths of 660 km beneath the earth's surface, and observables changes in plate motions at the earth's surface. The purpose of this study is determine, 1) how surface plate motions and the state of stress within surface plates react to, and provide feedbacks for, slab dynamics in the transition, 2) what is the origin of deep slab seismicity, and 3) if the observed shape of slabs is related to intrinsic properties of the subducting plate and plate boundary, or is instead a reflection of the time-dependent evolution of the slab. While the focus of this study is on deformation within the earth?s mantle, this deformation couples to the motions of plates at the earth's surface, which can cause destructive earthquakes and tsunamis.To address these questions with will develop three-dimensional numerical models (simulations) of subduction dynamics. More specifically we will use the best laboratory and observational constraints on the mineral composition of the plate (the crust, the residual harzburgite and the mantle layers), phase transitions (including all major mineral components) and rheology of the plate and mantle. We will enable dynamically mobile plates and plate boundaries, which are essential for understanding the physical connection between slab deformation and surface plate motions. These models eliminate several simplifying assumptions used in previous studies allowing us to make connections between slab deformation and surface plate motions and slab seismicity. Model results will be compared to global data sets on slab shape, plate characteristics and kinematics, as well as regional seismic observations on the state of stress within slabs and seismic discontinuities (which occur at phase transitions) across subducting lithosphere. The results of this project will provide a much more complete and realistic understanding of the physical processes that control the deformation of slabs and their ability to pull tectonic plates, and insight into how slab seismicity is related to the larger scale deformation slabs. In addition, the research will support the training of a PhD student, contribute software to the modeling community, introduce undergraduate students to scientific research, and contribute to the material used in undergraduate instruction.