Probing the Earth's Outer Core for a Stratified Layer

核-地幔边界科学跨越地震学、动力学、地球化学、地磁学和矿物物理学等地球深部学科。深部地球科学中的一个悬而未决的问题是，铁核和硅酸盐地幔之间是否会发生化学反应。这些在核-地幔边界(CMB)的化学反应将导致可以用地震波探测到的最外核和最下地幔的精细分层。最近的地球化学、动力学和地磁学方面的考虑支持核侧分层，但这样的层并没有被明确地成像。更好地分辨最外层的核结构有可能：(A)在许多领域产生研究活动，这些研究活动依赖于对核的准确了解，以及(B)帮助地球科学家更好地解决与行星当前化学状态有关的问题。对最外层核的地震研究依赖于SmKS波：地幔S波，当进入地核时转换为P波，从CMB底部反射m-1次，然后转换回S波，用于最后的地幔支段。SmKS震相是唯一在最外层具有转折深度的地震波。过去的工作表明，外核顶部的P速度降低，然而，SmKS相可能受到较低的地幔不均质性的严重污染。此外，稳定分层的外核层必须密度较低，因此预测这样的层的速度将会提高，而不是降低。因此，研究人员试图更好地显示最外层的地核，同时解释异常的地幔结构。我们的目标是以前所未有的细节从地震学上研究地球最外层的细微尺度结构，探测和表征(如果存在)任何外核分层(或确定其不存在)。我们首先寻求更好地描述影响SmKS的不均匀最低地幔的特征。在现有的全地幔层析成像模型的基础上，我们试图通过纳入大大增加的SmKS数据集来完善我们对最低地幔的理解，这些数据集来自(A)最近区域和全球地震部署的新SmKS数据，这些数据是使用为处理大数据量而优化的聚类算法获得的，以及(B)其他两个地震学家的现有数据集。我们将同时反演三维地幔结构和一维外核速度，以评估是否需要更新的一维参考模型，同时考虑到地幔深部的不均一性。我们还将正演宽带SmKS波场的模型方面，这些波场强烈地依赖于岩心最外层10？S处的P波速度和密度。这些实验将包括模拟S4KS-S3KS和S3KS-S2KS时间，以及出生？S2KS和S3KS波。这些波形模拟实验将包括一维和二维合成地震记录预测、阵列分析和反卷积算法，以锐化到达？每一张图都将使我们能够绘制出中巴下方的任何精细结构图。这个项目将揭示核-地幔反应的性质，这是理解地球演化的基础。该提案的一个独特特点是将断层成像工具与详细波形建模工具相结合，为大多数提案参与者提供交叉培训。

Core-mantle boundary science spans the deep Earth disciplines of seismology, dynamics, geochemistry, geomagnetism, and mineral physics. An outstanding question in deep Earth science is whether or not the iron core and silicate mantle chemically react with each other. These chemical reactions at the core-mantle boundary (CMB) would result in fine-scale outermost core and lowermost mantle layering that could be detected using seismic waves. Recent geochemical, dynamical, and geomagnetism considerations have supported core-side layering, but such a layer has not been unambiguously imaged. Better resolving outermost core structure has the potential of (a) spawning research activities in a number of fields that depend on accurate knowledge of the core, and (b) helping geoscientists better resolve issues relating to the current chemical state of the planet.Seismic studies of the outermost core rely on SmKS waves: mantle S-waves that convert to P-waves upon entering the core, reflect m-1 times from the underside of the CMB, then convert back to an S-wave for the final mantle leg. SmKS phases are the only seismic waves that have turning depths in outermost core. Past work indicates reduced P velocities at the top of the outer core, however, SmKS phases can be significantly contaminated by lower mantle heterogeneities. Also, a stably stratified outer core layer must be less dense, and hence predicts that the velocity of such a layer will be elevated, not decreased. Thus, the investigators seek to better image the outermost core, while accounting for anomalous mantle structure. Our goal is to seismically study the fine scale structure of Earth?s outermost core in unprecedented detail, to detect and characterize (if present) any outer core layering (or establish its absence). We first seek to better characterize the heterogeneous lowermost mantle that affects SmKS. Building on an existing whole mantle tomographic model, we seek to refine our understanding of the lowermost mantle by including a vastly increased data set of SmKS arrivals from (a) new SmKS data from recent regional and global seismic deployments obtained using a clustering algorithm optimized for processing large data volumes, and (b) existing data sets of two other seismologists. We will simultaneously invert for 3D mantle structure and 1D outer core velocity to assess the need for an updated 1D reference model while accounting for deep mantle heterogeneity. We will also forward model aspects of the broadband SmKS wavefield that depend strongly on the P-wave velocity and density in the outermost 10?s of km of the core. These experiments will include modeling S4KS-S3KS and S3KS-S2KS times, and the ?birth? of the S2KS and S3KS waves. These waveform-modeling experiments will include 1- and 2-D synthetic seismogram predictions, array analyses, and deconvolution algorithms to sharpen arrivals ? each of which will permit us to map any fine scale structure just beneath the CMB. This project will reveal properties of core-mantle reactions which are fundamental to understanding the evolution of the Earth. A unique feature of this proposal is combining the tools of tomography with those of detailed waveform modeling which offers cross-training for most of the proposal participants.