Collaborative Research: Structure and Dynamics of ultralow-velocity zones at the core-mantle boundary

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。地球岩石地幔和金属内核之间的边界是部分熔融结构拼凑而成的集合。这些结构，其特点是尖锐的山峰和山谷，是相对薄（10公里厚），密集（高达10%的密度比周围的岩石），并在空间上与下地幔的上升流区域相关。地震波在穿过这些结构时会变慢。因此，这些构造的指纹在穿过地球深部的地震信号中表现为超低速带（ULVZ）。除了它们独特的地震特征外，ULVZ也可能在化学上与周围的地幔岩不同。超低频带并非被动的，它与上覆地幔的剧烈运动有很强的耦合作用，而上覆地幔的剧烈运动会消耗地球内部的热量，驱动板块构造，并导致地表的火山活动。这项研究将研究地震信号，以揭示超低频带内的精细结构，并利用流体力学原理模拟超低频带内部分熔融物质剧烈运动所产生的结构，并产生通过模拟ULVZ结构传播的合成地震信号。这些调查的结果将回答一些基本问题的热量和物质的运输跨越地球的核幔边界和化学性质和物理性质的ULVZ.High分辨率的地震ScP和PcP波形数据提供了丰富的信息，当地结构的ULVZ。这种薄的，高密度层在地球的地幔的基础上，可能会发挥重要作用，在确定的位置和稳定性的地幔柱产生的核幔边界。此外，该地区也可能作为一个非常重要的阶段，在任何正在进行的质量之间的地球的外核和mantle.In本项目中，我们建议开发一个组合的地球动力学地震调查的内部结构和动力学的ULVZ。我们采用现有的和新的高分辨率偏移和建模的ScP和PcP波形，以更好地约束波的速度，层的地形，并在核幔边界的基础上ULVZ内的密度对比。我们将建立一个两阶段的地球动力学模型，首先将ULVZ建模为在地幔底部扩展的薄的自引力层。使用这个重力流模型和观测到的地形，我们可以预测的粘度的ULVZ，也推断的程度内的ULVZ的熔化。在第二阶段，我们将开发一个多相，多组分模型的岩浆混合和小尺度对流内的ULVZ。由此产生的模型提供了限制熔体存储和质量传递的ULVZ内的外核和下地幔。由此产生的模型将被纳入2D和3D正演合成地震图模拟，以测试与观测数据的一致性，并通过识别地表可见的诊断波形效应，更好地指导未来的ULVZ地震调查。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)The boundary between Earth's rocky mantle and metallic core is home to a patchwork collection of partially molten structures. These structures, characterized by sharp peaks and valleys, are relatively thin (10s of km in thickness), dense (up to 10% denser than the surrounding rocks), and are spatially correlated with regions of upwelling flow in the lower mantle. Seismic waves slow down as they pass through these structures. Consequently, the fingerprint of these structures appear as UltraLow Velocity Zones (ULVZ) in seismic signals traveling through Earth's deep interior. Besides their unique seismic signature, ULVZ are also likely to be chemically distinct from the surrounding mantle rock. Far from being passive, ULVZ are strongly coupled with the vigorous motion in the overlying mantle that dissipates Earth's internal heat, drives plate tectonics, and causes volcanism on the surface.This research will study seismic signals to unravel the fine scale structure within the ULVZ, simulate the structure arising from vigorous motion of the partially molten material within the ULVZ using principles of fluid mechanics, and create synthetic seismic signals traveling through the simulated ULVZ structure. The result of these investigations will answer a number of fundamental questions on heat and matter transport across Earth's core-mantle boundary and the chemical nature and physical properties of the ULVZ.High resolution seismic ScP and PcP waveform data provides a wealth of information regarding the local structure of the ULVZ. Such thin, high density layers at the base of Earth's mantle are likely to play a major role in determining the location and stability of mantle plumes generating from the core-mantle boundary. In addition, this region is also likely to serve as an extremely important stage in any ongoing mass transfer between Earth's outer core and the mantle.In this project we propose to develop a combined geodynamic-seismic investigation of the internal structure and dynamics of the ULVZ. We employ existing and new high resolution migration and modeling of ScP and PcP waveforms to better constrain wave velocities, layer topography, and density contrasts within ULVZ at the base of the core mantle boundary. We will develop a two-stage geodynamic model, beginning by modeling the ULVZ as a thin, self gravitating layer spreading at the bottom of the mantle. Using this gravity current model and the observed topography, we can predict the viscosity of the ULVZ and also infer the extent of melting within the ULVZ. In the second stage, we will develop a multiphase, multicomponent model of magma mixing and small scale convection within the ULVZ. The resulting model provides constraints on melt storage and mass transfer within the ULVZ both with the outer core and lower mantle. The resulting models will be built into 2D and 3D forward synthetic seismogram simulations to test consistency with observed data and to better guide future seismic investigation of ULVZ by identifying diagnostic waveform effects visible at the surface.