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CSEDI Collaborative Research: Joint seismic-geodynamic constraints on deep Earth structure - Implications for mantle convection and Earth rotation

CSEDI合作研究：地球深层结构的联合地震-地球动力学约束——对地幔对流和地球自转的影响

基本信息

批准号：
1903108
负责人：
Alessandro Forte
金额：
$ 32.62万
依托单位：
University of Florida
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-06-15 至 2024-05-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1903108&HistoricalAwards=false
关键词：
CSEDI Collaborative Research Joint seismic

项目摘要

The Earth's gravity field, which is precisely mapped by orbiting satellites, has 'bumps and valleys' where the field is stronger and weaker. The variation of this field on the very longest wavelengths describes the elliptical shape of the Earth. This elliptical figure is important because it determines the location of the axis of rotation that passes through the Earth's center and also controls changes in inclination of the Earth relative to the sun, owing to the gravitational 'pull' from the moon, the sun, and other planets. The Earth, in effect, behaves as a spinning top that can oscillate and wobble in complex ways. These changes in axial rotation and inclination affect how much solar energy ('insolation') is received at different latitudes on Earth, especially in the polar regions, and therefore has a major impact on climate and how it changes over long time intervals. A major problem in geophysics is to determine how the elliptical form of the Earth is generated by forces deep inside our planet. These forces also drive the horizontal motions of Earth's tectonic plates and the geological 'drift' of continents, as well as vertically pushing and pulling the continents and oceans up and down over time. Despite more than thirty years of progress by geophysicists who map lateral changes in Earth structure deep inside our planet using seismic waves, and similar progress by computational geophysicists who use these maps to model the internal forces needed to explain the motions of tectonic plates and the 'bumps' in Earth's gravity field, there remains a difficulty in properly accounting for the flattening of the elliptical figure of the Earth that is seen by satellites. The principal investigators (PIs) in this proposal will directly tackle this outstanding challenge by using both earthquake and gravity data, and data describing the topography of the Earth and the movements of tectonic plates, to obtain new maps of Earth's internal structure and new determinations of the forces that can explain all these data simultaneously. The outcome of this work will allow the PIs to specifically tackle the current challenge of accounting for Earth's long-term elliptical figure, how it changes with time, and how it influences high-latitude insolation and hence climate over long times. Powerful computer resources will be deployed to carry out this study over the next three years, employing a collaborative team of researchers from the Universities of Texas and Florida. This work will provide opportunities for training new graduate students who will learn state-of-the-art techniques in computer modelling and will develop advanced expertise in the geophysical sciences. The results of this work will be shared with a broad community of scientists, students and the general public with web-based platforms, communications in conferences and workshop, and in outreach activities.Key questions regarding the large-scale structure and dynamics of the mantle remain outstanding, despite three decades of progress in global seismic imaging of Earth's interior. There are longstanding difficulties in satisfactorily accounting for the very longest wavelength anomalies in Earth's gravity field, which are related to Earth's elliptical figure, with significant implications for Earth's time-dependent rotational dynamics. Questions concerning heterogeneity in the transition zone and the nature of "large low shear velocity provinces" (LLSVP) in the lower mantle, also continue to be elusive. These uncertainties regarding anomalous mantle structures directly impact our understanding of the global-scale dynamics of the Earth. To address the questions, the principal investigators propose a multidisciplinary effort to derive a new generation of tomography models that match a wide suite of surface data related to present-day structure and convective flow in the mantle, and can also constrain the time-dependent evolution of the mantle throughout the Cenozoic. To pursue these objectives the PIs will: (i) jointly invert global seismic and convection-related data with greatly improved coverage of 3-D mantle structure, incorporating geodynamic responses to lateral viscosity variations and topography on the discontinuities at the top and bottom of the transition zone; (ii) apply data assimilation methods to the new joint tomography models to reconstruct the Cenozoic evolution of 3-D mantle structure; (iii) calculate corresponding changes of Earth's moment of inertia, to be used in reconstructions of true polar wander and Milankovitch orbital cycles that are implicated in long-term climate variations. It is anticipated these new joint tomography models will provide improved constraints on the impact of transition-zone heterogeneity on convective mass and heat transport across this key region and on the spatial distribution of anomalous density structures within the LLSVP. This work will also contribute to resolving a longstanding difficulty concerning the origin of Earth's anomalous elliptical figure and the implications for the phase and amplitude of Milankovitch climate cycles in the geological past.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地球的重力场由轨道卫星精确地绘制，在磁场较强和较弱的地方有“颠簸和山谷”。这个场在最长波长上的变化描述了地球的椭圆形状。这个椭圆形很重要，因为它决定了通过地球中心的旋转轴的位置，也控制了地球相对于太阳的倾斜度的变化，这是由于月球，太阳和其他行星的引力“拉”。实际上，地球就像一个旋转的陀螺，可以以复杂的方式振荡和摆动。这些轴向旋转和倾斜的变化影响了地球上不同纬度地区，特别是极地地区接收到的太阳能（“日射”），因此对气候及其在长时间间隔内的变化有重大影响。地球物理学的一个主要问题是确定地球的椭圆形是如何由我们星球深处的力量产生的。这些力量还驱动着地球构造板块的水平运动和大陆的地质“漂移”，以及随着时间的推移垂直地推动和拉动大陆和海洋。尽管地球物理学家用地震波绘制了地球内部结构的横向变化，并且计算地球物理学家用这些地图模拟了解释构造板块运动和地球重力场“颠簸”所需的内力，在正确解释卫星所看到的地球椭圆形变平方面仍然存在困难。本提案中的主要研究人员将通过使用地震和重力数据以及描述地球地形和构造板块运动的数据来直接应对这一突出的挑战，以获得地球内部结构的新地图和可以同时解释所有这些数据的力的新测定。这项工作的结果将使PI能够专门解决目前的挑战，即解释地球的长期椭圆形，它如何随时间变化，以及它如何影响高纬度日射，从而长期影响气候。强大的计算机资源将被部署在未来三年内进行这项研究，雇用来自德克萨斯大学和佛罗里达大学的研究人员合作小组。这项工作将为培训新的研究生提供机会，他们将学习计算机建模方面的最新技术，并将发展地球物理科学方面的先进专门知识。这项工作的成果将通过网络平台、会议和讲习班上的交流以及外联活动与广大科学家、学生和公众分享。尽管地球内部的全球地震成像已经取得了三十年的进展，但有关地幔大尺度结构和动力学的关键问题仍然悬而未决。长期以来，在令人满意地解释地球重力场中的最长波长异常方面存在着困难，这些异常与地球的椭圆形有关，对地球随时间变化的旋转动力学具有重要意义。关于过渡带的不均匀性和下地幔“大的低剪切速度区”（LLSVP）的性质的问题也仍然是难以捉摸的。这些关于异常地幔结构的不确定性直接影响我们对地球全球尺度动力学的理解。为了解决这些问题，主要研究人员提出了一个多学科的努力，以获得新一代的层析成像模型，匹配广泛的表面数据，涉及到现今的结构和对流在地幔，也可以约束整个新生代地幔的时间依赖性演化。为实现这些目标，项目研究员将：㈠联合反演全球地震和对流相关数据，大大提高三维地幔结构的覆盖范围，纳入对横向粘度变化的地球动力学反应和过渡带顶部和底部不连续面上的地形; ㈡对新的联合层析成像模型应用数据同化方法，重建三维地幔结构的新生代演变;计算地球转动惯量的相应变化，用于重建与长期气候变化有关的真正的极移和米兰科维奇轨道周期。预计这些新的联合层析成像模型将提供改进的约束过渡区的异质性对流质量和热量输送的影响，在这个关键区域和异常密度结构的空间分布LLSVP。这项工作还将有助于解决一个长期存在的难题，即地球异常椭圆形的起源，以及对地质历史中米兰科维奇气候周期的相位和振幅的影响。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。