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

地球表面构造板块的运动是由地幔内的力引起的：扩张的山脊处的正浮力的推动和俯冲带处的下沉板块（板块）的拉力。在地球表面，这些力会导致地震，其中两个板块相互滑动（板块边界）。下沉板块产生的力有效拉动其后面的构造板块的能力取决于板块在地幔内如何变形，而这又取决于其变形时其材料特性如何变化。此外，与板片下沉相关的总力取决于矿物晶体结构的变化（相变），这会导致板片内密度的变化。 大多数相变发生在地表以下 410 至 660 公里之间，该区域称为过渡带。最终，地幔内下沉板片的变形表现为地表以下660公里深度的板片内发生的地震活动，以及地球表面板块运动的可观测变化。本研究的目的是确定：1​​）表面板块运动和表面板块内的应力状态如何对转变过程中的板片动力学做出反应并提供反馈，2）深部板片地震活动的起源是什么，以及3）观察到的板片形状是否与俯冲板块和板块边界的内在特性有关，或者是板片随时间演化的反映。虽然这项研究的重点是地幔内的变形，但这种变形与地球表面板块的运动耦合，可能导致破坏性地震和海啸。为了解决这些问题，我们将开发俯冲动力学的三维数值模型（模拟）。更具体地说，我们将使用最好的实验室和观测约束来限制板块的矿物成分（地壳、残余方辉橄榄岩和地幔层）、相变（包括所有主要矿物成分）以及板块和地幔的流变学。我们将实现动态移动的板块和板块边界，这对于理解板块变形和表面板块运动之间的物理联系至关重要。这些模型消除了先前研究中使用的几个简化假设，使我们能够在板片变形和表面板块运动以及板片地震活动之间建立联系。模型结果将与板片形状、板块特征和运动学的全球数据集以及俯冲岩石圈板片内应力状态和地震不连续性（发生在相变时）的区域地震观测进行比较。该项目的结果将提供对控制板变形及其拉动构造板块的能力的物理过程的更完整和现实的理解，并深入了解板地震活动与更大规模变形板的关系。此外，该研究还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.