Probing the Earth's Outer Core for a Stratified Layer

探测地球外核的分层层

• 批准号: 0944357
• 负责人: Christine Houser
• 金额: $ 11.38万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-12-01 至 2011-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0944357&HistoricalAwards=false
• 关键词: Probing; Earth; Outer; Core; Stratified

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.

核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。在地球深部科学中，一个悬而未决的问题是铁核和硅酸盐地幔是否会发生化学反应。 这些在核幔边界（CMB）的化学反应将导致精细尺度的最外层核和最下层地幔分层，可以使用地震波检测。 最近的地球化学，动力学和地磁的考虑支持核心侧分层，但这样一个层还没有明确的形象。 更好地解析最外层地核结构具有以下潜力：（a）在依赖于对地核的准确了解的许多领域中催生研究活动;（B）帮助地球科学家更好地解决与地球当前化学状态有关的问题。地幔S波在进入地核时转换为P波，从CMB的下侧反射m-1次，然后在最后的地幔段转换回S波。 SmKS相是唯一在最外层核中具有转向深度的地震波。 过去的工作表明，减少P速度在顶部的外核，然而，SmKS阶段可以显着污染下地幔的非均质性。 此外，稳定分层的外芯层必须密度较低，因此预测这样的层的速度将升高，而不是降低。 因此，研究人员试图更好地成像最外层的核心，同时解释异常地幔结构。 我们的目标是地震研究地球的精细结构？的最外层核心前所未有的细节，以检测和表征（如果存在）任何外部核心分层（或建立其缺席）。 我们首先寻求更好地描述影响SmKS的异质最低地幔。 建立在现有的全地幔层析成像模型，我们试图完善我们的理解，包括一个大大增加的数据集SmKS到达（a）新的SmKS数据从最近的区域和全球地震部署使用聚类算法优化处理大数据量，和（B）现有的数据集的其他两个地震学家。 我们将同时反演3D地幔结构和1D外核速度，以评估是否需要更新的1D参考模型，同时考虑深部地幔的不均匀性。 我们还将向前模型方面的宽带SmKS波场，强烈依赖于P波的速度和密度在最外层10？的核心。 这些实验将包括建模S4 KS 3 KS和S3 KSS 2KS时间，和？出生？S2 KS和S3 KS波。这些波形模拟实验将包括1-和2-D合成地震记录预测，阵列分析，和反褶积算法，以锐化到达？每一个都能让我们绘制出中巴之下的任何精细结构。 该项目将揭示地核-地幔反应的性质，这是理解地球演化的基础。 该提案的一个独特之处是将断层扫描工具与详细的波形建模工具相结合，为大多数提案参与者提供交叉培训。