EAR-PF: Shear Wave Splitting based on 3D Seismic Wave Simulations: Forward to Inverse Modeling of Upper Mantle and D" Anisotropy

Neala Creasy博士已获得NSF博士后奖学金，在科罗拉多矿业学院（CSM）开展研究和教育计划。她将通过利用地震产生的地震波来研究地幔在高压和高温下如何变形。解释这些地震波以及它们如何直接与地幔内的这些变形和矿物学过程相关是困难的，部分原因是由于在高压和高温下进行矿物物理实验所固有的必要假设和基本限制。她将计算合成波形的三维，现实的地球，探索如何地震观测与地幔变形。虽然一些先前的研究已经探索了用于简化这些观测的一些假设的可行性，但还有许多其他方面需要充分探索，以充分了解地球的复杂性。了解地球如何通过地幔对流变形是很重要的，因为这种变形控制着板块构造的表面表现，以火山活动和地震的形式。这项研究将有助于澄清如何利用地震波来了解地球地幔中的电流过程的全部潜力的一般理解。她的教育计划包括担任CSM研究生和本科生的研究导师，创作教育材料（例如，此外，丹佛大学还提供了一系列的信息图表、教学材料和虚拟现实（VR）设置，以激发年轻科学家从事基础科学研究，并通过IRIS（地震学研究机构联合会本科生实习计划）和丹佛科学博物馆等组织在当地社区继续开展外联工作。限制地球中地震各向异性的模式和性质有助于揭示矿物物理学、地幔对流和地震学之间的关系。岩石圈各向异性的来源，如冻结各向异性、过渡带和D”，使横波分裂测量复杂化，导致横波分裂不同于板块运动。如果我们更好地理解源自岩石圈的地震各向异性，我们也可以更好地约束D”各向异性，这需要在一定程度上对上地幔进行校正。射线理论是常用的，在一定的范围内是适当的，但不是所有的影响都已探讨。射线理论是一种无限频率近似，其有效性取决于波的周期、非均匀性的尺度、传播路径的长度以及多次波到达的叠加，这使得解释地震各向异性观测更加困难。数值方法和高性能计算的进步提供了新的机会，在进行地震观测研究时，利用逼真的三维地球结构考虑波传播的全部物理过程。在这项工作中，Creasy博士将探索剪切波分裂的假设，并通过3D全球波传播求解器SPECFEM3D_GLOBE进行数值模拟，梳理出不同模型和地球内各向异性观测之间的差异。这项工作将有助于提高对地震各向异性观测如何与地幔变形模型以及地壳、上地幔和D”各区域各向异性源相关的理解。这些见解将有助于阐明不同的地震各向异性观测技术在区域（如北美和澳大利亚）和全球尺度之间的差异。这项工作还将有助于在全球全波形反演中使用剪切波分裂的发展，解决适当的参数化，以描述反演过程中地幔中的体波各向异性。该奖项反映了NSF的法定使命，并被认为是值得支持的，通过使用基金会的智力价值和更广泛的影响审查标准进行评估。

Dr. Neala Creasy has been granted an NSF EAR postdoctoral fellowship to carry out research and educational plans at Colorado School of Mines (CSM). She will investigate how the Earth's mantle deforms under high pressures and temperatures by making use of the seismic waves produced by earthquakes. Interpreting these seismic waves and how they directly relate to these deformation and mineralogical processes within the mantle is difficult, in part due to necessary assumptions and fundamental limitations inherent to mineral physics experiments at high pressures and temperatures. She will calculate synthetic waveforms for a 3D, realistic Earth to explore how seismic observations relate to mantle deformation. While some prior research has explored the viability of some of the assumptions used to simplify these observations, there are many additional aspects that need to be fully explored to fully understand the complexity of the Earth. Understanding how the Earth deforms via mantle convection is important because this deformation controls the surface expression of plate tectonics, in the form of volcanic activity and earthquakes. This research will help clarify the general understanding of how to use seismic waves to their full potential in understanding current processes in Earth's mantle. Her educational plan involves acting as a research mentor for graduate and undergraduate students at CSM, creating educational material (e.g., infographics, teaching materials) and a Virtual Reality (VR) setup to excite young scientists to pursue basic science, and continued outreach efforts in the local community through organizations including IRIS (Incorporated Research Institutions of Seismology undergraduate internship program) and the Denver Museum of Science. Constraining the pattern and properties of seismic anisotropy in the Earth can help reveal relationships between mineral physics, mantle convection, and seismology. Sources of anisotropy in the lithosphere as frozen-in anisotropy, transition zone, and D" complicate shear wave splitting measurements, resulting in shear wave splitting that can differ from plate motion. If we better understand seismic anisotropy sourced in the lithosphere, we could also better constrain D" anisotropy, which requires correcting for the upper mantle to some extent. Ray theory is commonly used and is appropriate within certain limits, but not all implications have been explored. Ray theory is an infinite frequency approximation and its validity depends on the period of waves, the scale of heterogeneities, the length of its propagation path, and the superposition of multiple arrivals, making interpreting seismic anisotropy observations more difficult. Numerical methods and advances in high-performance computing offer new opportunities to take the full physics of wave propagation into account using realistic 3D Earth structures while conducting seismological observational studies. In this work, Dr. Creasy will explore the assumptions made in shear wave splitting as well as tease out discrepancies between different models and observations of anisotropy within the Earth, by conducting numerical simulations via 3D global wave propagation solver SPECFEM3D_GLOBE. This work will help improve the understanding of how seismic anisotropy observations are related to models of deformation in the Earth's mantle and the sources of anisotropy in the various regions of the crust, upper mantle, and D". These insights will help illuminate discrepancies between different seismic anisotropy observational techniques on regional (e.g. North America and Australia) and global scales. This work will also assist the development of using shear wave splitting in global full waveform inversion addressing appropriate parametrization to describe body-wave anisotropy in the mantle during the inversion process.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.