Investigating the Pervasiveness of Complex Seismic Anisotropy and Its Origin Beneath Continents

研究大陆下方复杂地震各向异性的普遍性及其起源

• 批准号: 1830644
• 负责人: Kelly Liu
• 金额: $ 21.19万
• 依托单位: Missouri University of Science and Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-01 至 2021-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1830644&HistoricalAwards=false
• 关键词: Investigating; Pervasiveness; Complex; Seismic; Anisotropy

Numerous geoscientific investigations over the past 50 years have convincingly demonstrated that the Earth's surface is divided into seven large and many small blocks known as tectonic plates. The relative movement of the plates against each other produces earthquakes, volcanoes, majestic mountains, and deep ocean basins. The physical and chemical processes that drive plate motion, however, are still poorly understood. Improving our understanding of such processes is essential not only for understanding how the Earth works, but also for achieving the ultimate goal of reliably predicting and mitigating natural hazard such as earthquakes and volcanic eruptions. One of the effective tools to investigate plate motion is shear wave splitting analysis, which is based on the observation that when a shear wave originated from an earthquake travels through an anisotropic area formed by plate motion, it will split into two waves. Previous shear wave splitting studies were mostly conducted under the assumption that there is only one layer of anisotropy. The recent dramatic increase in the number of seismic stations and recorded earthquakes suggests that the actual situation is more complicated than this single layer assumption. This project will develop and test a set of sophisticated tools to systematically investigate complex anisotropy on a global scale, for the purpose of providing constraints on a number of hypotheses related to plate dynamics and plate motion. This project will also support training of a graduate student, two undergraduate students, and a summer intern.Shear wave splitting (SWS) has been increasingly used to quantify seismic azimuthal anisotropy and to understand the geodynamic processes responsible for its formation. Mostly due to the limited amount of data available at most of the stations on Earth and the resulting poor azimuthal coverage of the incoming XKS (including SKS, SKKS, and PKS) rays, the vast majority of existing SWS studies, including most of the studies conducted by the PIs, assumed the simplest form of anisotropy, i.e., a single layer with a horizontal axis of symmetry. On the other hand, some SWS studies have identified systematic variations of the observed splitting parameters as a function of the azimuth of the incoming XKS rays. This dependence is the most important diagnostic of complex anisotropy (e.g., anisotropy with a dipping axis of symmetry and/or with two or more layers with a horizontal axis). By taking advantage of the recent dramatic increase in the quantity and quality of broadband seismic data, this project will address the important question of the pervasiveness of complex anisotropy using long-running seismic stations on the continents. The project also intends to characterize the complex anisotropy by determining the splitting parameters associated with the layers. The resulting spatial distribution of complex anisotropy will be a valuable constraint and input parameter for various geoscientific studies in the areas of geodynamic modeling, seismic tomography, and mineral physics.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.

过去 50 年来的大量地球科学研究令人信服地证明，地球表面分为七个大块和许多小块，称为构造板块。板块之间的相对运动会产生地震、火山、雄伟的山脉和深海盆地。然而，驱动板块运动的物理和化学过程仍然知之甚少。提高我们对这些过程的理解不仅对于理解地球如何运作至关重要，而且对于实现可靠预测和减轻地震和火山爆发等自然灾害的最终目标也至关重要。 研究板块运动的有效工具之一是剪切波分裂分析，它基于这样的观察：当源自地震的剪切波穿过板块运动形成的各向异性区域时，它将分裂成两个波。以前的剪切波分裂研究大多是在只有一层各向异性的假设下进行的。最近地震台数和记录地震数量的急剧增加表明，实际情况比这种单层假设更为复杂。该项目将开发和测试一套复杂的工具，在全球范围内系统地研究复杂的各向异性，目的是为与板块动力学和板块运动相关的许多假设提供约束。 该项目还将支持培训一名研究生、两名本科生和一名暑期实习生。剪切波分裂 (SWS) 已越来越多地用于量化地震方位各向异性并了解其形成的地球动力学过程。主要是由于地球上大多数站的可用数据量有限以及由此导致的传入 XKS（包括 SKS、SKKS 和 PKS）射线的方位角覆盖范围很差，绝大多数现有的 SWS 研究（包括大多数研究）由 PI 进行，假设最简单的各向异性形式，即具有水平对称轴的单层。另一方面，一些 SWS 研究已经确定了观测到的分裂参数的系统变化，作为入射 XKS 射线方位角的函数。这种依赖性是复杂各向异性（例如，具有倾斜对称轴和/或具有水平轴的两层或多层的各向异性）的最重要的诊断。通过利用最近宽带地震数据数量和质量的显着提高，该项目将利用大陆上长期运行的地震台来解决复杂各向异性普遍存在的重要问题。该项目还打算通过确定与层相关的分裂参数来表征复杂的各向异性。由此产生的复杂各向异性的空间分布将成为地球动力学建模、地震层析成像和矿物物理领域各种地球科学研究的宝贵约束和输入参数。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准。

项目成果

Mantle Flow in the Vicinity of the Eastern Edge of the Pacific‐Yakutat Slab: Constraints From Shear Wave Splitting Analyses

• DOI: 10.1029/2021jb022354
• 发表时间: 2021-09
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Yuchen Yang;Stephen S. Gao;Kelly H. Liu;F. Kong;Xiaofei Fu

Azimuthal anisotropy and mantle flow underneath the southeastern Tibetan Plateau and northern Indochina Peninsula revealed by shear wave splitting analyses

• DOI: 10.1016/j.tecto.2018.09.013
• 发表时间: 2018-11-13
• 期刊: TECTONOPHYSICS
• 影响因子: 2.9
• 作者: Kong, Fansheng;Wu, Jing;Gao, Stephen S.
• 通讯作者: Gao, Stephen S.

Metastable olivine within oceanic lithosphere in the uppermost lower mantle beneath the eastern United States

• DOI: 10.1130/g49879.1
• 发表时间: 2022-04
• 期刊: Geology
• 影响因子: 5.8
• 作者: F. Kong;Stephen S. Gao;Kelly H. Liu;Yinxia Fang;Hejun Zhu;R. Stern;Jiabiao Li

A Database of Shear‐Wave Splitting Measurements for the Arabian Plate

• DOI: 10.1785/0220180144
• 发表时间: 2018-09
• 期刊: Seismological Research Letters
• 影响因子: 3.3
• 作者: S. Qaysi;Kelly H. Liu;Stephen S. Gao

Spatial Variations of Upper Crustal Anisotropy Along the San Jacinto Fault Zone in Southern California: Constraints From Shear Wave Splitting Analysis

• DOI: 10.1029/2020jb020876
• 发表时间: 2020-08
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Enyuan Jiang;Kelly H. Liu;Yuan Gao;Xiaofei Fu;Stephen S. Gao