Love-wave propagation in oceanic upper mantle: constraints on radial anisotropy and implications for dynamics of the asthenosphere

海洋上地幔中的拉夫波传播：径向各向异性的约束及其对软流圈动力学的影响

• 批准号: 1538229
• 负责人: James Gaherty
• 金额: $ 22.86万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1538229&HistoricalAwards=false
• 关键词: Love; wave; propagation; oceanic; upper

The mechanisms that enable plate-like behavior on the Earth's surface and the processes that control plate motion are not fully understood. This study uses earthquake-generated seismic waves that were recorded by seafloor seismometers deployed for year in the central Pacific to probe the structure, particularly near the base of the plate. Using known relationships between deformation-induced mineral alignment and its effect on seismic signature, the degree of coupling between the plate and the underlying mantle will be evaluated. The question of how a rigid tectonic plate differs from the underlying mantle and whether or not these materials move in unison at the base of the plate, or not, has long intrigued Earth scientists. It is at the heart of understanding plate tectonics. The graduate student supported by this award will receive training in forefront marine seismic data analysis and have the opportunity to work with a unique dataset.Strong azimuthal seismic anisotropy in the Pacific lithosphere is consistent with observations of olivine alignment found in ophiolites, and it constrains models of ocean spreading center dynamics. In contrast, high-amplitude radial anisotropy observed in the Pacific asthenosphere provides evidence for a highly deformed and/or partially molten layer beneath the plate that may decouple the plate from the underlying mantle. A 600x400 km ocean bottom seismometer (OBS) array, located on ~70 Ma lithosphere, provided high-quality broadband seismic data, sufficient to characterize anisotropy with resolution (in depth and laterally) that is unattainable from global analyses. Rayleigh-wave velocities indicate extremely strong azimuthal anisotropy developed during formation of the lithosphere, but notably weaker azimuthal anisotropy is indicated in these data for the underlying asthenosphere. Determining the corresponding depth distribution of radial anisotropy requires detailed analysis of Love waves. Using a novel analysis of the wavefield, Love wave fundamental- and higher-mode phase velocities will be measured across the OBS array. Combined with the existing azimuthal anisotropy constraints, the resulting estimates of anisotropy will allow us to explicitly test whether flow-induced olivine fabric is consistent with the observations, or whether oriented melt is required to explain the observations.

使地球表面的板块行为和控制板块运动的过程的机制还没有完全理解。这项研究使用地震产生的地震波，这些地震波是由部署在太平洋中部多年的海底地震仪记录的，以探测该结构，特别是靠近板块底部的结构。利用已知的变形引起的矿物排列及其对地震特征的影响之间的关系，将评估板块和下伏地幔之间的耦合程度。一个刚性的构造板块与下面的地幔有何不同，以及这些物质在板块底部是否一致移动，这些问题一直困扰着地球科学家。它是理解板块构造的核心。该奖项支持的研究生将接受前沿海洋地震数据分析的培训，并有机会使用独特的dataset.Strong方位地震各向异性在太平洋岩石圈是一致的观察橄榄石对准发现蛇绿岩，它限制了海洋扩张中心动力学模型。相比之下，在太平洋软流层观察到的高振幅径向各向异性提供了证据，高度变形和/或部分熔融层下的板块，可能会解耦板块从下面的地幔。 位于约70 Ma岩石圈上的600 x400 km海底地震仪阵列提供了高质量的宽带地震数据，足以以全球分析无法达到的分辨率（深度和横向）表征各向异性。瑞利波速度表明岩石圈形成过程中发展的极强的方位各向异性，但明显较弱的方位各向异性表明在这些数据的底层软流圈。确定径向各向异性的相应深度分布需要对Love波进行详细的分析。使用一种新的波场分析，乐甫波的基本模式和更高的模式相速度将测量整个OBS阵列。 结合现有的方位角各向异性的约束，由此产生的各向异性的估计将使我们能够明确地测试是否流动诱导橄榄石织物是与观察一致，或者是否需要定向熔体来解释观察。