Collaborative Research: A Study of Deep Subduction Integrating Broadband Seismology and Mineral Physics

板块构造的发现使人们的注意力集中在地球内部的动态性质上。第一级问题之一是俯冲板块和地幔过渡带之间的相互作用，地幔过渡带是分隔上地幔和下地幔的410-660公里深的关键层。特别是，下降到下地幔的板块物质的数量对于了解地球内部的热对流和化学混合是至关重要的。虽然研究表明俯冲板块通常深入到下地幔深处，但实验岩石力学、计算机模拟和集中地震观测的一些最新结果都表明，由于重要成分的存在，快速俯冲的冷板块可能会在地幔过渡带变得浮力。来自5个不同机构的研究人员进行了一项新的合作研究，试图了解板块向下进入地球的过程中到底发生了什么。为了回答这些根本问题，研究人员将重点放在影响板块命运的两个关键问题上：1)地球内部(660公里长的不连续面)关键边界的性质，包括俯冲带附近的地形和密度对比；2)与深部地震相关的岩石类型和密度的变化如何标志着板块在向下下降时停滞不前，特别是被快速推入地球的板块。这个项目正在通过整合来自自然、实验实验室和计算机模拟的数据来研究这些问题。正在研究的自然实验室是西太平洋沿线的深俯冲带，数百万年来，古老的寒冷板块一直在那里迅速俯冲。这些区域提供了一个特殊的环境来研究地球深处俯冲板块发生了什么。地震学家正在利用深部地震的精确分布、它们的断层模式以及它们周围岩石中地震波的特性来研究俯冲板块。对于实验部分，矿物物理实验室正在研究如何通过地球深处不同岩石类型中晶体的图案和排列来解释地震观测。研究人员还通过观察岩石在受到强烈压力和高温时的行为，来检查板块向下进入地球内部时是否会变得脆弱。为了将自然和实验结果置于适当的背景下，先进的板块俯冲计算机模拟正在研究成分、温度、密度和粘度等性质变化对地球动力学的影响。该项目每年为三名研究生提供培训，这项工作的协作性质确保他们的培训将得到极大的丰富和扩大。除了跨学科研究的广泛背景外，还包括对普通受众的教育和宣传。在教育多媒体可视化中心的帮助下，正在创建一个动画教学模块，以说明板块俯冲的各种场景，重点是板块与地幔过渡带的相互作用。

The discovery of plate tectonics has focused attention to the dynamic nature of the Earth's interior. One of the first-order issues is the interaction between subducted plates and the transition zone of the mantle, a key layer at 410-660 km depth that divides the upper and lower mantle. In particular, the amount of plate material that descends into the lower mantle is central to understanding thermal convection and chemical mixing of the Earth's interior. While studies have suggested that subducted plates generally penetrate deep into the lower mantle, a number of recent results from experimental rock mechanics, computer simulations, and focused seismic observations all suggest that cold, rapidly subducting plates may become buoyant in the mantle transition zone due to the presence of important compositional components. A new collaborative study by researchers from 5 different institutions is seeking to understand what is really happening to plates as they travel down into the Earth. To answer these fundamental questions, the researchers are focusing on two key issues affecting the fate of plates: 1) The nature of a key boundary in the Earth's interior (660-km discontinuity), including its topography and density contrast near subduction zones; 2) how changes in rock type and density associated with deep earthquakes appear to mark pieces of plate that stagnated on their downward descent, particularly for plates driven down into the earth quickly. This project is investigating these questions by incorporating data from nature, the experimental laboratory, and computer simulations. The natural laboratories being examined are the deep subduction zones along the western Pacific, where old, cold plate has been rapidly subducting for millions of years. These areas provide an exceptional environment to examine what happens to subducting plates deep within the Earth. Seismologists are studying the subducted plates using the precise distribution of deep earthquakes, their faulting patterns, and the properties of the seismic waves in the rocks that surround them. For the experimental component, the mineral physics laboratory is investigating how seismic observations can be explained by patterns and alignment of crystals within different rock types from great depth in the Earth. Researchers are also examining whether plates become weak as they travel down into the Earth's interior by looking at how rocks behave when they are subjected to intense pressure and heat. To place the natural and experimental results in proper context, advanced computer simulations of plate subduction are investigating the geodynamic effects of changes in properties like composition, temperature, density, and viscosity. This project is providing training for three graduate students per year, and the collaborative nature of the work ensures that their training will be significantly enriched and broadened. In addition to the broad context of the interdisciplinary research, there is a component of education and outreach for the general audience. An animated teaching module is being created with help from the Educational Multimedia Visualization Center in order to illustrate various scenarios of plate subduction, focusing on the plate interaction with the mantle transition zone.