Seismic Imaging of the Inner Core Boundary Region

拟议工作的目的是通过分析地震产生的地震波来更好地了解地球固体内核和液体外核之间的边界。对核心内部边界(ICB)区域的地震分析提供了独特的约束条件，补充了实验室和计算实验对高温高压下核心组件特性的影响。ICB区的精细结构与理解核的动力学和演化特别相关，因为它代表了核的Fe、Ni、轻元素化学中的相界。对ICB的地震约束也与研究地球磁场的地球动力学家有关，因为它们指导外核对流模型的边界条件和驱动力的选择。建议的研究涉及绕射(PkP_Cdiff)和散射(PKiKP尾波)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台阵构建的。利用全波理论进行正演，估算了不同频率下的视Pkp{cdiff}射线参数，并对下地核径向速度模型进行了相应的色散曲线反演。为了寻找ICB地区的横向构造变化，对短周期射线参数估计进行了微分意义上的分析(以Pkp_(Df)为参考)。与相应的差分走时观测相比，这种差分射线参数估计对较低的地幔不均一性的敏感性要低得多。国际监测系统的各种小口径阵列站正在更新PI的临界点前PKiKP波形数据库，并正在应用一种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，以模拟数据并比较临界前PKiKP尾波的四个潜在来源的相对贡献：下地幔的不均一性、CMB地形、上部内核的不均一性和ICB地形。大部分拟议资金将用于支持一名博士生和几名本科生研究助理。学生们将有机会参加科学会议，成为同行评议出版物的作者或合著者。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国际地球物理研究所教授的研究生地球物理课程中讨论和应用。拟议工作的主题将在私人助理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时，与各个K-12小组进行非正式讨论。

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.