CSEDI collaborative research: a multidisciplinary approach to investigate the origin of anisotropy at the base of the mantle

CSEDI 合作研究：采用多学科方法研究地幔底部各向异性的起源

• 批准号: 1067513
• 负责人: Barbara Romanowicz
• 金额: $ 38.32万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1067513&HistoricalAwards=false
• 关键词: CSEDI; collaborative; research; multidisciplinary; approach

Seismic anisotropy (i.e. seismic waves travel in different directions at different speeds) in the deeper earth was discovered in the mid-sixties and was soon interpreted in a qualitative way as a result of crystal alignment during convection (LPO). This concept since became generally accepted. More recently strong anisotropy and heterogeneity was documented in the lowermost mantle adjacent to the metallic and liquid core. This enigmatic D" zone is both a thermal and chemical boundary layer characterized complex dynamic processes that are reflected in many intriguing seismic observations. Much progress was recently achieved in mineral physics, to characterize elastic and deformation properties of lowermost mantle minerals including the post-perovskite phase. Advances in geodynamic modeling now allow us to track the strain evolution during mantle convection. As a result, there are now precise ways to compute synthetic seismograms in a 3D anisotropic earth down to body wave frequencies. Our proposed study follows on preliminary work started 2 years ago, and is focused on the forward modeling of LPO anisotropy in D", with the goal of combining tools and observations developed by geodynamicists, seismologists and mineral physicists, in order to gain better understanding of the origin of seismic anisotropy in D", and determine which microscopic and macroscopic processes may be at play. In our work to-date, we have set up a multi-step procedure for this purpose, which combines five modeling ingredients in a logical chain: (1) For a particular hypothesis regarding mantle dynamics, geodynamical models provide information on the macroscopic strain deformation accommodated by individual packets of mantle material. (2) This strain deformation information is then used as boundary conditions for numerical models that calculate the resulting mineralogical texture (i.e. LPO) within a polycrystalline mineral aggregate. (3) Seismic elastic constants, determined from mineral properties and preferred orientations, are applied to numerous mineral aggregates throughout the region of interest, (4) followed by forward seismic modeling through the 3D elastic anisotropic model acquired from steps 1-3. (5) Resulting models and seismic waveforms are compared to available seismic observations. Our initial results illustrate that we can use macroscopic observations to constrain plausible constituents and deformation mechanisms. So far, our work has focused on 2D models of a subducting slab reaching the core-mantle boundary (CMB) and its subsequent spreading along the CMB. We here propose to extend our set of geodynamic tools to the 3D case, which will allow us to explore the predicted distribution of different kinds of anisotropy at the base of the mantle in a more realistic framework and confront the resulting seismic wavefields to available broadband seismic data. We will perform experiments and theoretical mineral physics computations. This project promotes interdisciplinary work and cross-education in the fields of geodynamics, mineral physics and seismology among the PI's, participating students and postdoctoral associates, stimulating learning to solve complex scientific problems by sharing different expertise. It will also provide suggestions for future seismic experiments targeted at better characterizing anisotropy in D".

在六十年代中期发现了地震各向异性（即地震波以不同速度以不同速度的不同方向行进），并因对流过程中的晶体对准（LPO）很快以定性的方式解释。此后，这个概念已被普遍接受。最近，强烈的各向异性和异质性记录在与金属和液体芯相邻的最低地幔中。这个神秘的d“区域既是一个热和化学边界层，表征了复杂的动态过程，这些过程反映在许多有趣的地震观察中。最近在矿物质物理学中取得了许多进步，以表征我们最低地幔矿物的弹性和变形特性，包括perovskite阶段的最低弹性，包括在perovskite阶段，包括在当前的型号中的过力。 2年前，我们提出的研究在3D各向异性地球上计算合成地震图的方式始于初步工作，并重点介绍了D中的LPO各向异性的远期建模。 d“，并确定哪些显微镜和宏观过程可能会发挥作用。在我们迄今为止的工作中，我们为此目的建立了一个多步骤的程序，该过程结合了逻辑链中的五种建模成分：（1）关于地幔动力学的特定假设，地球动力学模型可在单独的材料中提供摩croccopocopopic axpopopic temantic的信息。 （2）然后将此应变变形信息用作数值模型的边界条件，这些模型计算了多晶矿物聚集体中所得的矿物学纹理（即LPO）。 （3）根据矿物质和优选方向确定的地震弹性常数应用于整个感兴趣区域的许多矿物聚集体，（4），然后通过从步骤1-3获得的3D弹性各向异性模型通过3D弹性各向异性模型进行正向地震建模。 （5）将结果模型和地震波形比较与可用的地震观测。我们的最初结果表明，我们可以使用宏观观测来限制合理的成分和变形机制。到目前为止，我们的工作集中在到达核心壳边界（CMB）的俯冲板的2D模型上，随后沿CMB扩散。我们在这里建议将我们的地球动力学工具扩展到3D情况，这将使我们能够在更现实的框架中探索在地幔底部的各种各向异性的预测分布，并与可用的可用宽带地震数据对抗。我们将执行实验和理论矿物物理计算。该项目促进了PI，参与的学生和博士后同事的地球动力学，矿物质物理学和地震学领域的跨学科工作和交叉教育，从而刺激学习通过共享不同专业知识来解决复杂的科学问题的学习。它还将为未来的地震实验提供建议，该实验的目标是更好地表征D“中的各向异性。