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

随着EarthScope的USArray和其他密集地震阵列的出现，我们有了一个前所未有的机会来研究地球深处的地震结构，一直到地核。探测地球最深处的结构为了解地球化学和热历史的许多方面提供了必要的限制。这笔拨款将资助阵列成像技术的进一步发展，这将允许更详细地调查如何以及为什么在这么深的地方有如此复杂的结构，以及它们如何与地球的进化联系起来。该基金将资助一名博士后和一名研究生，并促进欧洲的持续国际合作。通过对下地幔的地震相位采样，我们发现了超低速度带（ULVZs）、可能与钙钛矿相关的D”层、大低剪切速度省（LLSVPs）和原始物质在核幔边界（CMB）上的滚动山丘。基于动力学和矿物学的地幔模型与深部地震观测相适应的研究已经取得了长足的进展，但仍缺少许多细节。目前还不确定ulvz的密度和速度是否与可能的部分熔化有关，或者是否有不同的化学起源，但回答这个问题所需的物理性质信息很少。例如，用于成像ulvz的主要相位SPdKS对密度不是特别敏感，并且速度与结构的形状有很强的权衡。其他地震观测显示，观测到的D？层：后钙钛矿层在快区下面最厚，在慢区下面消失。然而，很难区分地幔基底洋岩石圈俯冲引起的速度梯度效应和相边界效应。来自USArray和其他阵列的数据集，特别是更大的PICASSO（部分由NSF-CD和CAREER资助）阵列的数据集，显示了所有范围的波形复杂性，并且具有显著的覆盖范围。这项拨款将为更好地约束地幔结构和回答以下问题提供资金：(1)我们能否解决和区分不同弹性特性之间的权衡？(2)我们能确定超视场的三维几何形状吗？(3) CMB中除了超低速带外，是否还存在其他类型的低速带？(4)推断出的板块历史与下地幔构造的存在是否相容？(5) D的关系是什么？还有地幔深处的板块？(5)我们如何解决llsvp的边缘问题？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路径检测器（MPD）来优化当前的层析模型，并生成与观测波形复杂性相匹配的合成地震图。这些下地幔构造的物理尺寸及其推断的地震参数将用于地幔对流地球动力学模型，并在CMB条件下进行矿物物理实验。这些进一步的矿物物理和地球动力学实验将使我们更好地了解俯冲板块之间的联系，D？层，ulvz和llsvp以及深部地幔的动态演化。

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.