Seismic Imaging of the Inner Core Boundary Region

这项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。内岩心边界（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岩心组分性质的实验室和计算实验。ICB区域的精细结构对理解地核的动力学和演化特别重要，因为它代表了地核中铁、镍和轻元素化学的相边界。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。提出的研究涉及衍射（PKP_Cdiff}）和散射（临界PKiKP尾da）地震能量。PKP_Cdiff}数据集是由世界各地存在的许多临时和永久宽带地震阵列构建的。利用全波理论求解下外核径向速度模型的正演问题，估计了不同频率下PKP_{Cdiff}射线的表观参数，并反演了相应的频散曲线。正在以差分方式分析短周期射线参数估计（使用PKP_{DF}作为参考），以寻找ICB区域的横向结构变化。与相应的差分走时观测相比，这种差分射线参数估计对下地幔非均质性的敏感性要低得多。目前正在利用国际监测系统的各种小孔径阵列站更新PI的临界PKiKP波形数据库，并正在应用非线性曲线拟合技术来量化尾波衰减率的变化。PI正在利用单散射技术合成PKiKP尾波包线，对数据进行建模，并比较四个潜在的临界前PKiKP尾波源的相对贡献：下地幔的非均质性、CMB地形的非均质性、内核上部的非均质性和ICB地形。大部分提议的资金将用于支持一名博士生和几名本科生研究助理。这些学生将有机会参加科学会议，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，将在网上提供。与提议的工作相关的技术将在PI教授的研究生地球物理学课程中讨论和应用。在PI作为地球与大气科学系地球科学部的外联代表的角色中，拟议工作的主题将以非专业术语与各个K-12小组进行讨论。

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.