Collaborative Research: NSFGEO-NERC: Advancing capabilities to model ultra-low velocity zone properties through full waveform Bayesian inversion and geodynamic modeling

合作研究：NSFGEO-NERC：通过全波形贝叶斯反演和地球动力学建模提高超低速带特性建模能力

• 批准号: 2341237
• 负责人: Michael Thorne
• 金额: $ 56.04万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-04-01 至 2027-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2341237&HistoricalAwards=false
• 关键词: Collaborative; Research; NSFGEO; NERC; Advancing

This proposal will improve the description of features called Ultra-Low Velocity Zones (ULVZs). ULVZs are thin patches of material that sit on the Earth’s core-mantle boundary (CMB), which is at a depth of 2891 km (1796 miles). As their name implies, ULVZs slow passing seismic waves by as much as 50%. This makes which makes them some of the most anomalous features of the Earth’s interior. Several ULVZs are beneath some of Earth’s largest hot spot volcanoes, such as Hawaii, Iceland, and Samoa. Imaging of the Earth’s interior shows that hot rising materials, or mantle plumes, connect these volcanoes from ULVZs to the surface. But the origin, lifetime, size, and composition of these ULVZs are not known, nor is their role in the formation of the mantle plumes. This project will provide greater details as to where these features exist, their formation and composition. This work analyzes two types of seismic waves sensitive to thin ULVZ layering that interact with and bounce off these ULVZ features. The study focuses on an area beneath the western Pacific Ocean because of extensive seismic data coverage and known ULVZs in the region. The project will create a new seismic database built from public records and networks in South Korea, Taiwan, and Japan. This database will then enable imaging of ULVZ structures at the CMB using modern statistical capabilities. Computer simulations of mantle flow will help interpret the formation, motion, and role in mantle processes of the ULVZs. This project includes an annual outreach STEM event for K-8 students for the local Utah Pacific Island community. This event will include activities to teach about the mantle plumes that form Pacific Islands through hot spot volcanism.Ultra-Low Velocity Zones (ULVZs) are structures with strongly reduced seismic velocities at Earth’s core-mantle boundary (CMB) which have been associated with or linked to hot-spot volcanism, Large Igneous Provinces, core-mantle interaction, downwelling subduction and Large-Low Velocity Provinces (LLVPs) and thus are a critical component of global mantle dynamics. ULVZs are typically studied using waveform analysis of ULVZ-sensitive seismic probes (e.g., SPdKS, ScP, ScS), but previous studies suffer from large uncertainties in ULVZ parameters due to modeling trade-offs and lack a geophysical inference of ULVZs through rigorous parameter estimation. This project will develop a transformative waveform inversion approach and apply it to characterize ULVZ properties including their seismic velocities, density, size, and shape. Specifically, the project will (1) collect a new database of ULVZ-sensitive ScP and PcP waveforms utilizing publicly available seismic array data as well as new data from South Korea, Taiwan, Japan, and the International Monitoring System (IMS) arrays, (2) advance capabilities for full waveform Bayesian inversion for ULVZ properties to quantitatively distinguish regions with and without ULVZ structures (i.e., Bayesian model selection), and to perform joint inversion of ScP and PcP waveforms, (3) quantify the waveform effects from 2-D/3-D ULVZ structures, (4) search for additional, previously unlooked-for arrivals in the ScP wavefield consistent with 3-D ULVZ structure using array processing approaches, and (5) relate observed ULVZ localities and properties to lowermost mantle flow and dynamics through 3D geodynamic models. This is a collaborative proposal between scientists at the University of Utah, Arizona State University, and Leeds University, and is therefore co-funded by the National Science Foundation (NSF) and the United Kingdom’s Natural Environment Research Council (NERC).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.

该提案将改进对超低速区 (ULVZ) 特征的描述，超低速区是位于地球核心-地幔边界 (CMB) 上的薄层物质，深度为 2891 公里（1796 英里）。顾名思义，超低电压区使地震波的传播速度减慢了 50%，这使得它们成为地球内部最异常的特征之一。 ULVZ 位于地球上一些最大的热点火山下方，例如夏威夷、冰岛和萨摩亚。地球内部的成像显示，炽热的上升物质或地幔羽流将这些火山从 ULVZ 与地表连接起来。这些 ULVZ 的大小和组成尚不清楚，它们在地幔柱形成中的作用也不清楚，该项目将提供有关这些特征存在的位置、其形成和组成的更多详细信息。地震波对与这些 ULVZ 特征相互作用并反弹的薄 ULVZ 层敏感。该研究重点关注西太平洋下方的区域，因为该地区拥有广泛的地震数据覆盖范围和已知的 ULVZ。然后，该数据库将利用现代统计功能对 CMB 的 ULVZ 结构进行成像，这将有助于解释地幔的形成、运动和作用。该项目包括为犹他州当地太平洋岛屿社区的 K-8 学生举办的年度外展 STEM 活动，该活动将包括教授有关通过热点火山作用形成太平洋岛屿的地幔柱的活动。区域（ULVZ）是地球核心-地幔边界（CMB）处地震速度大幅降低的结构，与热点火山活动有关或相关，大型火成岩省、核心-地幔相互作用、下降流俯冲和大低速省 (LLVP) 因此是全球地幔动力学的重要组成部分，通常使用 ULVZ 敏感地震探测器（例如 SPdKS、ScP、 ScS），但之前的研究由于建模权衡而导致 ULVZ 参数存在很大的不确定性，并且缺乏通过以下方式对 ULVZ 进行地球物理推断：该项目将开发一种变换波形反演方法，并将其应用于表征 ULVZ 特性，包括地震速度、密度、大小和形状。具体来说，该项目将 (1) 收集 ULVZ 敏感 ScP 和的新数据库。 PcP 波形利用公开的地震阵列数据以及来自韩国、台湾、日本和国际监测系统 (IMS) 阵列的新数据，(2) 全波形贝叶斯反演的高级功能对于 ULVZ 区域，定量区分有和没有 ULVZ 结构（即贝叶斯模型选择），并对 ScP 和 PcP 波形进行联合反演，(3) 量化 2-D/3-D ULVZ 结构的波形影响，( 4 ) 使用阵列处理方法搜索与 3-D ULVZ 结构一致的 ScP 波场中其他先前未发现的到达信号，以及 (5) 关联观察到的 ULVZ 位置这是犹他大学、亚利桑那州立大学和利兹大学科学家之间的合作提案，因此由美国国家科学基金会 (NSF) 和美国国家科学基金会 (NSF) 共同资助。英国自然环境研究理事会 (NERC)。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。