NSFGEO-NERC: Global ultralow-velocity zone properties from seismic waveform modeling

NSFGEO-NERC：地震波形建模的全球超低速区特性

• 批准号: 1723007
• 负责人: June Wicks
• 金额: $ 3.64万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-01 至 2021-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1723007&HistoricalAwards=false
• 关键词: NSFGEO; NERC; Global; ultralow; velocity

This project aims to image the Earth's deep interior using recordings of seismic waveforms generated by earthquakes occurring globally. Constraining the structure, composition and dynamic motions of the deep Earth, from which we have no definitive rock samples, is crucial to understanding both the forces that are actively shaping our Earth from formation to present, and hazards such as surface volcanism that arise from deep within the Earth. This study focuses on technical development of a new modeling approach combining data analysis and prediction of seismic waveforms, which will be applied to imaging features at the core-mantle boundary called ultralow-velocity zones (ULVZs). The existence of these ULVZs is well documented, and several past studies have linked them to important global Earth processes, such as melting, influx of core iron into the mantle, or the leftover remnants from a molten Earth early in its history. Yet what ULVZs physically represent remains in question. This research is aimed at determining what ULVZs are in terms of their composition, location, and relation to past and present processes inside the Earth. This work will provide crucial constraints on understanding how the Earth formed, what the ongoing dynamic motions within the Earth currently are, and how these motions are related to surface hot spot volcanism such as Hawaii and Yellowstone. This project aims to develop a new seismic waveform modeling approach that will allow for a new understanding of the origin of the complex seismic waveforms we routinely record from earthquakes worldwide and how these seismic waves are sensitive to small-scale features within the Earth. The methods and software developed in this project will be shared openly and will be applicable to a broad range of researchers who may wish to apply these techniques to different target areas. In addition, this research benefits a large area of researchers who work on determining Earth structure and processes and how they relate to surface processes. This project establishes a new international collaborative research effort between the United Kingdom and the USA and will support the training of two post-doctoral researcher fellows, one in the UK and one in the USA.The specific project goal is to develop a transformative joint waveform modeling and data analysis approach to characterize global ULVZ structure. The primary tasks are to (1) collect a new global database of seismic waveforms sensitive to ULVZ structure, (2) use recent developments in seismic wavefield modeling that includes full-wave sensitivity kernels and differential wavefield mapping to determine the sensitivity of seismic arrivals to ULVZ structure and to identify additional seismic arrivals that may be utilized to study ULVZ properties, (3) further the development of wavefield modeling approaches using a fast 3-D Born waveform modeling approach in order to predict seismic waveforms for any desired input model, which allows for (4) the determination of global ULVZ structure through a Bayesian probabilistic inversion, and (5) assess the physical origin of ULVZs by testing current mineral physics models of ULVZs. The approach represents an entirely new line of interrogating localized structures in the deep Earth. The ultimate aim of this work is to fundamentally reassess ULVZs from all angles, and reduce uncertainties in their properties, location, and composition. Ultimately this project will produce a global assessment of ULVZ existence as well as to determine their compositional and geographic scope, and how they are related to other dynamic features inside the Earth.

该项目的目的是利用全球地震产生的地震波形记录，对地球深层内部进行成像。 限制地球深部的结构，组成和动态运动，我们没有确定的岩石样本，对于理解从形成到现在积极塑造我们地球的力量以及从地球深处产生的地表火山活动等危险至关重要。 本研究的重点是技术开发的一种新的建模方法相结合的数据分析和预测的地震波形，这将被应用到成像功能的核幔边界称为超低速带（ULVZ）。 这些ULVZ的存在是有据可查的，过去的几项研究将它们与重要的全球地球过程联系起来，例如熔化，核心铁流入地幔，或早期熔融地球的残余物。 然而，超低电压区实际上代表什么仍然是一个问题。这项研究的目的是确定什么是ULVZ的组成，位置以及与地球内部过去和现在的过程的关系。 这项工作将提供至关重要的限制，了解地球如何形成，目前正在进行的动态运动在地球内，以及这些运动是如何与表面热点火山活动，如夏威夷和黄石公园。 该项目旨在开发一种新的地震波形建模方法，这将使我们能够对我们从全球地震中常规记录的复杂地震波形的起源以及这些地震波如何对地球内的小尺度特征敏感有新的理解。 该项目开发的方法和软件将公开共享，并将适用于希望将这些技术应用于不同目标领域的广泛研究人员。 此外，这项研究有利于大面积的研究人员谁的工作，以确定地球的结构和过程，以及它们如何与表面过程。该项目在英国和美国之间建立了一个新的国际合作研究工作，并将支持两名博士后研究员的培训，一名在英国，一名在美国。具体项目目标是开发一种变革性的联合波形建模和数据分析方法，以表征全球ULVZ结构。 主要任务是（1）收集对ULVZ结构敏感的地震波形的新的全球数据库，（2）使用地震波场建模的最新发展，包括全波敏感性内核和差分波场映射，以确定地震波至对ULVZ结构的敏感性，并识别可用于研究ULVZ特性的额外地震波至，（3）使用快速3-D玻恩波形建模方法进一步开发波场建模方法，以便预测任何期望的输入模型的地震波形，这允许（4）通过贝叶斯概率反演确定全球ULVZ结构，（5）通过检验现有的超低硫区矿物物理模型，评价超低硫区的物理成因。 这种方法代表了一种全新的询问地球深部局部结构的方法。 这项工作的最终目的是从根本上从各个角度重新评估ULVZ，并减少其属性，位置和成分的不确定性。最终，该项目将对超低电压区的存在进行全球评估，并确定其组成和地理范围，以及它们与地球内部其他动态特征的关系。