Using Dense Seismic Arrays to Map Sharp Features in the Deep Mantle

使用密集地震阵列绘制地幔深部的清晰特征

• 批准号: 1345015
• 负责人: Meghan Miller
• 金额: $ 18.7万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-07-01 至 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1345015&HistoricalAwards=false
• 关键词: Using; Dense; Seismic; Arrays; Map

With the advent of EarthScope's USArray and other dense seismic arrays, there is an unprecedented opportunity for investigating the seismic structures within the deep Earth, all the way to the core. Detecting structures in the very deepest part of the Earth provide essential constraints in understanding many aspects of the chemical and thermal history of the planet. This grant will fund further development of array imaging techniques that will allow for more detailed investigation of how and why there are such complex structures at this great depth and how they link to the evolution of the Earth. The grant will provide support for a postdoc, a graduate student, and foster continued international collaborations in Europe.Observations of seismic phases sampling the lower mantle have suggested Ultra Low Velocity Zones (ULVZs), a possible perovskite to postperovskite related D" layer, Large Low Shear Velocity Provinces (LLSVPs), and rolling-hills of primordial material on the core-mantle boundary (CMB). Considerable progress has been made toward developing dynamical and mineralogical based mantle models compatible with seismic observations at the deep mantle, yet many details are still missing. It is still uncertain whether the densities and velocities of ULVZs are related to possible partial melting or have a distinct chemical origin, but the information about physical properties needed to answer this question are poorly constrained. For example the major phase used in imaging ULVZs, SPdKS, is not particularly sensitive to density and the velocities have strong trade-off with the shape of the structures. Other seismic observations have shown connections between the geographic distribution of the observed D? layer: where the post-perovskite layer is thickest beneath fast regions and disappears beneath slow regions. However, it is difficult to distinguish the velocity gradient effects caused subducted oceanic lithosphere at the base of the mantle from phase boundary effects. The data set from USArray and other arrays, especially the greater PICASSO (partially funded by NSF-CD and CAREER) array, display waveform complexity at all ranges with remarkable coverage. This grant will provide funding to better constrain mantle structures and answer questions such as: (1) Can we resolve and distinguish between the trade-off of different elastic properties? (2) Can we determine the 3D geometry of the ULVZ's? (3) Are there other types of low velocity zones besides ULVZs existing at CMB? (4) How compatible are the inferred slab histories with the presence of lower mantle structures? (5) What is the relationship between D? and slabs in the deep mantle? (5) How well can we resolve the edges of the LLSVPs? To answer those questions, we will use array seismology techniques, waveform modeling and the newly developed Multi-Pathing Detector (MPD) to sharpen current tomographic models and produce synthetic seismograms that match observed waveforms complexities. The physical dimensions of these structures in the lower mantle and their inferred seismic parameters will be used in geodynamic models of mantle convection and explored in mineral physics experiments at CMB conditions. These further mineral physics and geodynamic experiments will allow for improvement in our understanding of the connection between subducted slabs, the D? layer, ULVZs, and LLSVPs and the dynamic evolution in the deep mantle.

随着Earthscope的UsArray和其他密集的地震阵列的出现，有一个前所未有的机会来调查深层深地球内的地震结构，一直到核心。 在地球最深的部分中检测结构为理解地球的化学和热历史的许多方面提供了基本限制。 该赠款将资助阵列成像技术的进一步发展，这些技术将允许对这种巨大的深度以及它们如何与地球的演变联系起来进行更详细的研究。 The grant will provide support for a postdoc, a graduate student, and foster continued international collaborations in Europe.Observations of seismic phases sampling the lower mantle have suggested Ultra Low Velocity Zones (ULVZs), a possible perovskite to postperovskite related D" layer, Large Low Shear Velocity Provinces (LLSVPs), and rolling-hills of primordial material on the核心边界（CMB）已取得了相当大的进步Ulvz，SPDKS对密度并不特别敏感，并且速度在结构的形状上具有很强的权衡。其他地震观测表明，观察到的d的地理分布之间存在联系？层：玻璃后的层最厚的地方，在快速区域下方消失在慢速区域下。但是，很难区分速度梯度效应引起地幔底部的俯冲岩石圈与相边界效应。 来自USARRAY和其他阵列的数据集，尤其是大毕加索（部分由NSF-CD和职业）阵列，在所有范围内显示波形复杂性，并具有出色的覆盖范围。 该赠款将提供资金以更好地限制地幔结构并回答以下问题：（1）我们可以解决和区分不同弹性特性的权衡吗？ （2）我们可以确定ULVZ的3D几何形状吗？ （3）除CMB处的ULVZ以外，还有其他类型的低速区吗？ （4）推断的平板历史与较低地幔结构的存在如何兼容？ （5）D之间的关系是什么？和厚底地幔中的平板？ （5）我们可以如何解决LLSVP的边缘？ 为了回答这些问题，我们将使用阵列地震学技术，波形建模和新开发的多态探测器（MPD）来锐化当前的层析成像模型并产生匹配观察到波形复杂性的合成地震图。这些结构在下地幔及其推断的地震参数中的物理尺寸将用于地幔对流的地球动力学模型，并在CMB条件下进行矿物质物理实验中探索。 这些进一步的矿物质物理学和地球动力学实验将可以改善我们对俯冲板之间的联系，D？层，ULVZ和LLSVPS以及深陆台的动态演化。