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

随着EarthScope的USAray和其他密集地震阵列的出现，有一个前所未有的机会来调查地球深处的地震结构，一直到核心。 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。 这笔赠款将资助阵列成像技术的进一步发展，这将允许更详细的调查如何以及为什么在这个巨大的深度有如此复杂的结构，以及它们如何与地球的演变联系起来。 该补助金将为博士后，研究生提供支持，并促进在欧洲的持续国际合作。对下地幔采样的地震相位观测表明，超低速带（ULVZ），一个可能的钙钛矿到后钙钛矿相关的D”层，大低剪切速度区（LLSVP），以及核幔边界（CMB）上原始物质的滚动山丘。基于动力学和矿物学的地幔模型的发展已经取得了相当大的进展，但仍缺少许多细节。它仍然是不确定的密度和速度的ULVZ是否与可能的部分熔融或有一个独特的化学起源，但有关的物理特性的信息需要回答这个问题是不好的约束。例如，在成像ULVZ中使用的主要相位SPdKS对密度不是特别敏感，并且速度与结构的形状具有很强的权衡。其他地震观测显示，所观察到的D？层：其中后钙钛矿层在快区域下方最厚，并且在慢区域下方消失。然而，相边界效应与大洋岩石圈俯冲在地幔底部引起的速度梯度效应很难区分。 来自USAray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，显示了所有范围内的波形复杂性。 这笔拨款将提供资金来更好地约束地幔结构并回答以下问题：（1）我们能否解决和区分不同弹性特性的权衡？(2)我们能确定ULVZ的三维几何形状吗？(3)除了超低电压区外，中巴是否还有其他类型的低速区？(4)推断的板块历史与下地幔结构的存在有多大的一致性？(5)D之间的关系是什么？和地幔深处的板块(5)我们如何分辨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路径检测器（MPD），以锐化当前的层析成像模型，并产生与观测波形复杂性相匹配的合成地震图。这些结构在下地幔的物理尺寸和推断的地震参数将用于地幔对流的地球动力学模型，并在CMB条件下的矿物物理实验中进行探索。 这些进一步的矿物物理学和地球动力学实验将允许改进我们的理解俯冲板块之间的连接，D？层，ULVZ和LLSVPs和深部地幔的动力学演化。

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.