Constraining multi-scale interactions between slabs and mantle flow within Western Pacific subduction zones

俯冲带，一个构造板块俯冲到另一个板块之下，形成了地球上一些最戏剧性的山脉--以及一些最致命的地震和火山。在下地幔中，下降的板块被称为“板块”，它被更热的物质所包围，这些物质在地质时期表现为流体。围绕板块的地幔流动模式和速度决定了作用在板块和上覆板块上的力的方向和大小。这些力在驱动板块变形方面发挥了重要作用，包括造山和地震，但它们不能直接观察到。必须使用复杂的数学模型来估计它们。在这个项目中，霍尔特和他的团队将开发这样的模型，并运行几组计算来调查地幔流动及其对西太平洋地区板块和板块的影响。之所以选择这个区域，是因为有大量的数据可以用来检验模型计算，也因为平板和平板的几何形状很复杂(因此很有趣)。将具有这种复杂性的模型集成到全球范围的地幔流动模型中是一个巨大的技术挑战，Holt已经部分地解决了这一挑战。他的团队的新模型将首先解决地幔流动可能与旧的简化模型给出的估计值有多大差异的问题。在调整它们以与西太平洋的地质和地球物理数据保持一致后，这些模型将为这一复杂地区的地幔流动和板块作用力提供新的线索。PI和团队将开发和自由共享软件工具，为其他小组为类似复杂的地震多发地区(例如加勒比海和东南亚)建模打开了大门。这个项目将支持一名研究生和一名职业生涯早期的教授。这些模型和输出将用于向迈阿密大学地球动力学专业的学生教授模型可视化和数据分析。这一研究项目的首要目标是为地幔和岩石圈板块之间的相互作用开发一个机械框架，重点是几何结构复杂的西太平洋。这一框架将通过使用一套全球俯冲模型来预测主要西太平洋板块(例如千岛-日本、琉球-南开和伊豆-博宁-马里亚纳)附近的地幔流动状况和相关力量而建立。在该小组编制了对地幔动力学敏感的西太平洋观测数据数据库后，将运行包含高分辨率西太平洋板块和弱板块边界的全球数值模型，以量化与这些观测相一致的地幔流动和粘性场。该团队还将使用一套有针对性的数值测试来研究全球尺度流动和地幔流动局部化(由于幂定律粘性流变学)对流场和相关作用力的影响。将讨论与岩石圈-地幔流动相互作用有关的三个相互关联的问题。在区域尺度上：地幔是否从菲律宾海板块(PSP)下方流出，并产生决定西太平洋俯冲观测的力量？这种通过平板之间的狭窄缝隙发生的外流是否需要由于幂定律蠕变而实现流动局部化？在全球范围内：大规模地幔流动施加的力量是否强烈影响西太平洋板块(例如，它们是否产生日本板块的非常浅的倾角)？在解决这些问题时，这项研究将提供关于复杂的板块几何形状和全球规模的地幔流动对俯冲带机制的相对贡献的可转移洞察力。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Subduction zones, where one tectonic plate descends beneath another, are responsible for forming some of the Earth's most dramatic mountain ranges - and for some of its deadliest earthquakes and volcanoes. In the underlying mantle, where the descending plate is referred to as a “slab”, it is surrounded by hotter material which behaves as a fluid over geological time. The pattern and speed of mantle flow around the slab governs directions and magnitudes of forces acting on it and on the overlying plates. These forces play an important role in driving plate deformation, including mountain building and earthquakes, but they cannot be observed directly. They must be estimated, using sophisticated mathematical models. In this project, Holt and his team will develop such models and run several sets of calculations to investigate mantle flow and its effect on slabs and plates in the Western Pacific region. This region was chosen because there is abundant data that can be used to test the model calculations, and because the geometry of slabs and plates is complex (and hence interesting). Integrating a model with this complexity into a global-scale mantle flow model presents an immense technical challenge which has already been partially met by Holt. His group's new models will first address how much mantle flow may differ from estimates given by older, simplified models. After they have been adjusted to be consistent with geological and geophysical data from the Western Pacific, the models will shed new light on mantle flow and forces on plates in this complex region. The PI and team will develop and freely share software tools, opening the door for other groups to model similarly complex, earthquake-prone regions (e.g., the Caribbean and Southeast Asia). This project will support a graduate student and an early-career professor. The models and outputs will be used for teaching model visualization and data analysis to Geodynamics students at the University of Miami. The overarching goal of this research project is developing a mechanical framework for interactions between the mantle and lithospheric plates, with a focus on the geometrically complex Western Pacific. This framework will be developed by using a suite of global subduction models to predict the mantle flow regime and associated forces in the vicinity of the main Western Pacific slabs (e.g., Kuril-Japan, Ryukyu-Nankai, and Izu-Bonin-Mariana). After the team compiles a database of Western Pacific observables sensitive to mantle dynamics, global numerical models incorporating highly resolved Western Pacific slabs and weak plate boundaries will be run to quantify the mantle flow and viscosity fields consistent with these observations. The team will also use a suite of targeted numerical tests to examine how the flow-field and associated forces are impacted by both global-scale flow and mantle flow localization (due to a power-law viscous rheology). Three inter-linked questions related to lithosphere-mantle flow interactions will be addressed. At a regional scale: Does mantle out-flow from beneath the Philippine Sea Plate (PSP) occur and produce forces that dictate Western Pacific subduction observables? Does this out-flow, which occurs through narrow gaps between slabs, require flow localization due to power-law creep? At a global scale: Do forces imposed by large-scale mantle flow strongly impact the Western Pacific slabs (e.g., do they produce the very shallow dip of the Japan slab)? In addressing these questions, this study will provide transferrable insight on the relative contributions of complex slab geometries and global-scale mantle flow to subduction zone mechanics.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.