Seismic Imaging of the Inner Core Boundary Region

内核边界区域的地震成像

• 批准号: 0537438
• 负责人: Keith Koper
• 金额: --
• 依托单位: Saint Louis University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-04-01 至 2010-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0537438&HistoricalAwards=false
• 关键词: Seismic; Imaging; Inner; Core; Boundary

The aim of the proposed work is to achieve a better understanding of the boundary between the Earth's solid inner core and liquid outer core by analyzing earthquake-generated seismic waves. Seismic analysis of the inner core boundary (ICB) region provides unique constraints that complement laboratory and computational experiments on the properties of core components at high pressure and temperature. The fine structure of the ICB region is particularly relevant to understanding the dynamics and evolution of the core because it represents a phase boundary within the Fe, Ni, light-element chemistry of the core. Seismic constraints on the ICB are also relevant to geodynamicists who study Earth's magnetic field because they guide the selection of boundary conditions and driving forces for models of convection in the outer core. The proposed study involves diffracted (PKP_Cdiff}) and scattered (precritical PKiKP coda) seismic energy. The PKP_Cdiff} data set is being constructed from the many temporary and permanent broadband seismic arrays that exist around the world. Apparent PKP_{Cdiff} ray parameters are being estimated at various frequencies, and the corresponding dispersion curves are being inverted for radial velocity models of the lower outer core, using full wave theory to do the forward problem. Short period ray parameter estimates are being analyzed in a differential sense (using PKP_{DF} as a reference) to search for lateral structural variations in the ICB region. Such differential ray parameter estimates are much less sensitive to lower mantle heterogeneities than corresponding differential travel time observations. The PI's data base of precritical PKiKP waveforms is being updated using the various small aperture array stations of the International Monitoring System, and a non-linear curve-fitting technique is being applied to quantify variations in coda decay rates. The PI is synethesizing PKiKP coda envelopes with single-scattering techniques to model the data and to compare the relative contributions of four potential sources of precritical PKiKP coda waves: heterogeneities in the lower mantle, CMB topography, heterogeneities in the upper inner core, and ICB topography.Most of the proposed funds are being used to support a PhD student and several undergraduate research assistants. The students will have the opportunity to travel to scientific meetings and become authors or co-authors of peer-reviewed publications. The results from the proposed work, including relevant data sets, will be made available on the web. Techniques related to the proposed work will be discussed and applied in graduate geophysics classes taught by the PI. The subject of the proposed work will be discussed in lay terms to various K-12 groups as the PI performs his role as the outreach representative for the Geosciences section of the Department of Earth and Atmospheric Sciences.

拟议工作的目的是通过分析地震产生的地震波，更好地了解地球固体内核和液体外核之间的边界。内堆芯边界（ICB）区域的地震分析提供了独特的约束条件，补充了高压和高温下堆芯组件特性的实验室和计算实验。ICB区域的精细结构与理解核心的动力学和演化特别相关，因为它代表了核心的Fe，Ni，轻元素化学中的相边界。 ICB上的地震约束也与研究地球磁场的地球动力学家有关，因为它们指导了外核对流模型的边界条件和驱动力的选择。所提出的研究涉及衍射（PKP_Cdiff）和散射（前临界PKKP尾波）地震能量。PKP_Cdiff}数据集是由世界各地的许多临时和永久宽带地震台阵构成的。 利用全波理论进行正演，估算了不同频率下的PKP_{Cdiff}射线视参数，反演了外核下部径向速度模型的频散曲线。本文以PKP_{DF}为参考，对短周期射线参数估计进行了微分分析，以寻找ICB区的横向构造变化。这种差分射线参数估计比相应的差分走时观测对下地幔非均匀性的敏感性要低得多。正在利用国际监测系统的各种小孔径阵列台站更新PI的前临界PKiKP波形数据库，并应用非线性曲线拟合技术来量化尾波衰减率的变化。 PI正在用单次散射技术合成PKiKP尾波包络，以模拟数据并比较四种潜在的前临界PKiKP尾波源的相对贡献：下地幔的不均匀性，CMB地形，上内核的不均匀性和ICB地形。学生将有机会前往科学会议，并成为同行评审出版物的作者或共同作者。拟议工作的结果，包括相关数据集，将在网上公布。 与拟议工作相关的技术将在PI教授的研究生物理学课程中进行讨论和应用。拟议工作的主题将在各K-12小组中进行非专业讨论，因为PI将履行其作为地球和大气科学部地球科学科外联代表的职责。