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

俯冲带，一个构造板块下沉到另一个板块之下，形成了地球上一些最壮观的山脉，也产生了一些最致命的地震和火山。在下面的地幔中，下降板块被称为“板块”，它被较热的物质包围，这些物质在地质时期表现为流体。板块周围地幔流动的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（包括造山和地震）方面起着重要作用，但它们无法直接观测到。它们必须用复杂的数学模型来估计。在这个项目中，霍尔特和他的团队将开发这样的模型，并运行几组计算来研究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，是因为这里有丰富的数据可以用来测试模型计算，而且因为板和板的几何形状很复杂（因此很有趣）。将一个如此复杂的模型整合到一个全球尺度的地幔流模型中是一个巨大的技术挑战，Holt已经部分地解决了这个问题。他的小组的新模型将首先解决地幔流动与旧的简化模型给出的估计有多大不同。经过调整，使其与西太平洋的地质和地球物理数据保持一致后，这些模型将为这个复杂地区的地幔流动和板块作用力提供新的线索。PI及其团队将开发并免费共享软件工具，为其他组织模拟类似复杂的地震易发地区（例如加勒比和东南亚）打开大门。该项目将资助一名研究生和一名早期职业教授。这些模型和产出将用于迈阿密大学地球动力学专业的模型可视化和数据分析教学。这个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建立一个机械框架，重点是几何结构复杂的西太平洋。该框架将通过使用一套全球俯冲模型来预测西太平洋主要板块（如千岛岛-日本、琉球-南开和伊扎-波宁-马里亚纳）附近的地幔流动状况和相关力量来发展。在该团队编制了一个对地幔动力学敏感的西太平洋观测数据数据库之后，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，以量化与这些观测结果一致的地幔流动和粘度场。该团队还将使用一套有针对性的数值测试来检查流场和相关力是如何受到全球尺度流动和地幔流动局部化（由于幂律粘性流变）的影响的。将讨论与岩石圈-地幔流动相互作用有关的三个相互联系的问题。在区域尺度上：菲律宾海板块（PSP）下的地幔外流是否发生并产生了决定西太平洋俯冲观测结果的力量？由于幂律蠕变，这种通过板间狭窄间隙的流出是否需要流动定位？在全球范围内：大规模地幔流施加的力是否强烈影响西太平洋板块（例如，它们是否产生了日本板块的极浅倾角）？在解决这些问题的过程中，本研究将为复杂的板块几何形状和全球范围的地幔流动对俯冲带力学的相对贡献提供可转移的见解。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。

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.