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.

尚未完全了解地球表面上类似板的行为以及控制板运动的过程的机制。这项研究使用地震生成的地震波，这些地震波是在中太平洋部署年度的海底地震仪记录的，以探测结构，尤其是在板块底部附近。利用变形诱导的矿物对齐之间的已知关系及其对地震特征的影响，将评估板和下面地幔之间的耦合程度。刚性构造板与基础地幔以及这些材料是否在板块底部一致移动的问题，长期以来一直吸引了地球科学家。它是理解板块构造的核心。获得该奖项支持的研究生将接受最前沿的海洋地震数据分析的培训，并有机会与独特的数据集合作。太平洋岩石圈中的Strong Azimuthal地震各向异性与在Ophiolite中发现的橄榄石一致性的观察结果一致，并且它约束了海洋传播中心动力的模型。相反，在太平洋运动圈中观察到的高振幅径向各向异性为板下方的高度变形和/或部分熔融层提供了证据，该层可能使板从基础地幔中解脱出来。 位于〜70 mA岩石圈上的600x400 km海洋底部地震仪（OBS）阵列提供了高质量的宽带地震数据，足以表征具有分辨率（深度和侧向）的各向异性，而全球分析是无法实现的。瑞利波速度表明在岩石圈形成过程中开发了极强的方位角各向异性，但对于基础性动态圈，这些数据中指出了尤其是较弱的方位角各向异性。确定径向各向异性的相应深度分布需要对爱波的详细分析。使用对波场的新分析，将在整个OBS阵列中测量Love Wave基本相位和高模式相速度。 结合现有的方位角各向异性约束，对各向异性的估计值将使我们能够明确测试流动诱导的橄榄石织物是否与观测值一致，或者是否需要定向熔体来解释观察结果。