Anisotropic structure of Earth's inner core from noise correlations

从噪声相关性看地球内核的各向异性结构

• 批准号: 1620595
• 负责人: Xiaodong Song
• 金额: $ 24万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-01 至 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1620595&HistoricalAwards=false
• 关键词: Anisotropic; structure; Earth; inner; core

The Earth's solid inner core is formed from the crystallization of the liquid outer core as the Earth cools. The inner core possesses axisymmetric anisotropy with its fast axis aligned nearly North-South due to the preferred alignment of the inner core iron crystals in this direction. Previous studies of the inner core structure have shown great complexities. Thus, understanding the origin of this prominent anisotropy is one of the fundamental questions of earth science today; and imaging the complex three-dimensional anisotropic structure of the inner core is crucial in this endeavor. Unfortunately, seismic imaging of the deep Earth has been limited by the distribution of earthquake and station locations. This project seeks to explore a new technique that extracts a vastly different set of observations for the deep Earth based on correlations of seismic noise (from ambient environment and from earthquake coda). We expect that this improved inner core seismic model will benefit the mineralogical and the geodynamical communities, as it provides constraints on their models. The project has implications for understanding the origin of the anisotropy, composition, dynamics, and evolution of Earth?s core and the inner core in particular. The retrieval of the deep penetrating waves overcomes some of disadvantages of traditional earthquake-based methods, which will have a fundamental impact on revealing the structure of the Earth?s deep interior.This project builds on recent successes in extracting body waves from correlations of either ambient noise or earthquake coda. During the last decade, ambient noise correlation technique has been widely used to study the structure of our planet, in particular surface wave tomography of lithosphere structure. More recent studies have shown feasibility to extract body waves from correlations of ambient noise or earthquake coda. We have recently succeeded in retrieving clear triplicated PKP phases and inner-core arrivals PKIKP2 and PKIIKP2 simultaneously using stacks of empirical Green?s functions from autocorrelations of single station or cross-correlations between data recorded at different stations. These observations allow us to use differential travel times between different phases to eliminate or reduce the influence of mantle heterogeneity and source errors. The new PKIKP2 and PKIIKP2 data suggest a seismic anisotropy in the inner-inner core of the Earth that has a fast axis aligned near the equator and a different form of anisotropy from the North-South aligned anisotropy observed in the outer inner core. In this project, we seek to explore these new types of data to constrain the 3D anisotropic structure of the inner core. The differential PKP travel times between different branches from noise cross-correlations provide vastly different data coverage from existing earthquake data. The differential PKIIKP2- PKIKP2 travel times provide brand new samples of the deepest part of the inner core. Specifically, we will systematically retrieve PKIKP2 and PKIIKP2 simultaneously applying autocorrelations and cross-correlations to all available arrays around the world and systematically retrieve triplicated PKP branches by applying cross-correlations to pairs of station arrays at distances greater than 145 degrees. We will then combine the new noise-based data with earthquake data to model and invert for 3D inner-core anisotropic structure.

当地球冷却时，地球的固体内核是由液体外核的结晶形成的。内核具有轴对称各向异性，其快速轴的快速轴几乎向北对齐，这是由于内核铁晶体在该方向上的首选比对。对内部核心结构的先前研究表现出了很高的复杂性。因此，了解这种杰出的各向异性的起源是当今地球科学的基本问题之一。在这项工作中，成像内核的复杂三维各向异性结构至关重要。不幸的是，地震的地震成像受地震和站点位置的分布受到限制。该项目旨在探索一种新技术，该技术基于地震噪声的相关性（来自环境环境和地震尾巴）提取了深层地球的一组截然不同的观察结果。我们预计，这种改善的内部核心地震模型将使矿物学和地球动力学群落受益，因为它在其模型上提供了约束。该项目对理解各向异性，组成，动力学和地球核心尤其是内核的起源具有影响。深层穿透性波的检索克服了传统基于地震的方法的一些缺点，这将对揭示地球深内部的结构产生根本性的影响。该项目基于从环境噪声或地震尾巴的相关性提取身体波的最新成功基础。在过去的十年中，环境噪声相关技术已被广泛用于研究我们行星的结构，特别是岩石圈结构的表面波断层扫描。最近的研究表明，从环境噪声或地震尾声的相关性中提取体波的可行性。最近，我们成功地检索了清晰的三分一式PKP阶段，以及内核的到达PKIKP2和PKIIKP2，并使用经验绿色的堆栈从单个站点的自相关或在不同站点记录的数据之间的互相关中获得了经验绿色的功能。这些观察结果使我们能够在不同阶段之间使用差异旅行时间来消除或减少地幔异质性和源误差的影响。新的PKIKP2和PKIIKP2数据表明，地球内部核心的地震各向异性在赤道附近的快速轴对齐，并且与北 - 南北对齐的各向异性的各向异性形式不同。在这个项目中，我们试图探索这些新类型的数据，以限制内核的3D各向异性结构。噪声互相关的不同分支之间的差异PKP旅行时间与现有地震数据提供了巨大不同的数据覆盖率。差异PKIIKP2- PKIKP2旅行时间提供了内核最深部分的全新样品。具体而言，我们将系统地检索PKIKP2和PKIIKP2同时在世界各地的所有可用阵列中应用自相关和互相关，并系统地检索三重三重PKP分支，通过将交叉相关施加到位于距离阵列的距离对以大于145度的距离。然后，我们将将新的基于噪声的数据与地震数据结合起来，以建模并反转3D内核各向异性结构。

项目成果

Origin of temporal changes of inner-core seismic waves

• DOI: 10.1016/j.epsl.2020.116267
• 发表时间: 2020-07
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Yi Yang;Xiaodong Song

Amplitude and decay of long-period coda of great earthquakes

• DOI: 10.1016/j.pepi.2020.106538
• 发表时间: 2020-09
• 期刊: Physics of the Earth and Planetary Interiors
• 影响因子: 2.3
• 作者: H. Xia;Xiaodong Song;R. Weaver;Jiangtao Li

Reply to Yao et al.'s comment on “Origin of temporal changes of inner-core seismic waves”

• DOI: 10.1016/j.epsl.2020.116639
• 发表时间: 2021
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Yi Yang-;Xiaodong Song

Support for equatorial anisotropy of Earth’s inner-inner core from seismic interferometry at low latitudes

低纬度地震干涉测量支持地球内核的赤道各向异性

• DOI: 10.1016/j.pepi.2017.03.004
• 期刊: Physics of the Earth and Planetary Interiors
• 影响因子: 2.3
• 作者: Tao Wang;Xiaodong Song
• 通讯作者: Xiaodong Song

Ambient noise surface wave tomography of marginal seas in east Asia

• DOI: 10.26464/epp2017003
• 发表时间: 2017-06
• 期刊: Earth and Planetary Physics
• 影响因子: 2.9
• 作者: Qing Wang;Xiaodong Song;Jianye Ren