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部的作用力引起的：伸展脊处正浮力的推动和俯冲带处下沉板块（板块）的拉力。在地球表面，当两个板块相互滑动（板块边界）时，这些力就会导致地震。下沉板块所产生的力能否有效地拉动其背后的构造板块，取决于板块在地幔内的变形情况，而地幔的变形又取决于板块变形时其物质特性的变化情况。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），这导致板内密度的变化。这些相变大多发生在地球表面以下410至660公里之间，这个区域被称为过渡带。最终，地幔内下沉板块的变形表现为板块内地表以下660公里深处的地震活动，以及地表板块运动的可观测变化。本研究的目的是确定：1)地表板块运动和地表板块内部的应力状态如何对过渡时期的板块动力学作出反应，并为其提供反馈；2)深板块地震活动的起源是什么；3)观察到的板块形状是否与俯冲板块和板块边界的内在性质有关，或者是反映了板块的随时间演化。而这项研究的重点是地球内部的变形？这种变形与地球表面板块的运动相结合，可能导致破坏性的地震和海啸。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条件来研究板块的矿物组成（地壳、残余的辉锌矿和地幔层）、相变（包括所有主要矿物成分）以及板块和地幔的流变学。我们将使动态移动板块和板块边界成为可能，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。这些模型消除了以前研究中使用的一些简化假设，使我们能够在板块变形和地表板块运动以及板块地震活动之间建立联系。模型结果将与关于板块形状、板块特征和运动学的全球数据集，以及关于板块内部应力状态和地震不连续（发生在俯冲岩石圈的相变）的区域地震观测结果进行比较。该项目的结果将为控制板块变形及其拉板块能力的物理过程提供更完整和更现实的理解，并深入了解板块地震活动与更大规模变形板块的关系。此外，这项研究将支持博士研究生的培训，为建模社区提供软件，介绍本科生进行科学研究，并为本科生教学提供材料。

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.