Constraining depth dependent anisotropy in Australia through Ps Receiver function analysis, frequency-dependent shear wave splitting and forward modeling

大陆岩石圈见证了地球的地质和生物演化，为我们提供了前所未有的地球历史视角。虽然近年来我们对地球物理演化的许多方面的理解已经蓬勃发展，但我们对某些过程的知识仍然存在根本性的差距。一个特别的缺陷是我们对大陆的结构和地质演化的理解。虽然海洋岩石圈有一个生命周期，开始于洋中脊，结束于俯冲带，但我们仍然没有清楚地了解大陆岩石圈最初是如何形成的，或者为什么岩石圈在数十亿年的时间里保持稳定，尽管在后来的构造事件中经历了显着的变形。在澳大利亚，大陆岩石圈最古老的部分可以追溯到大约32亿年前，使其成为检验与大陆形成和演化有关的假设的绝佳地点。几十年来详细的地质研究限制了澳大利亚许多重大构造事件的发生时间。然而，用于推断构造变形信息的地震各向异性观测结果，讲述了一个关于澳大利亚岩石圈的故事，这个故事比从地表地质推断的要复杂得多。该项目的目标是利用新开发的地震学方法提供更详细和准确的地震各向异性图像，以帮助推断澳大利亚大陆内部的构造演化，从而更好地了解大陆形成、组装和演化的过程。澳大利亚地幔岩石圈和软流圈中各向异性结构的特征是一个长期存在的难题，主要是因为从不同的数据分析方法（SKS分裂与表面波层析成像）收集的推论经常相互冲突。该建议将应用频率相关SKS分裂分析和各向异性Ps接收器函数分析，以更精确地限制澳大利亚大陆下方各向异性的横向和深度变化。所提出的工作有三个具体目标：1）使用来自26个永久宽带站的数据来测量频率相关SKS分裂并应用Ps接收器功能分析，并且对于站的子集，进行结构的详细正演建模并比较这些站的子集的方法的结果。2)通过分析构造历史和背景方面的各向异性结构模型，调查澳大利亚下方深度相关各向异性的起源。3)通过与独立的深度相关模型的比较，了解澳大利亚下方方位各向异性面波模型和SKS分裂观测之间差异的来源。这项工作解决的一些具体的科学问题包括：各向异性如何随着澳大利亚大陆下的深度而变化？各向异性结构的变化是否与地质和/或构造结构相对应？地幔岩石圈的各向异性结构是否揭示了过去的变形事件？为什么以前的研究发现表面波层析成像模型和SKS分裂观测之间的差异？

The continental lithosphere has witnessed much of the Earth's geologic and biologic evolution, giving us an unprecedented view into our planet's history. While our understanding of many aspects of the physical evolution of the Earth has flourished in recent years, fundamental gaps in our knowledge of some processes persist. One particular deficiency is in our understanding of the structure and geologic evolution of continents. While oceanic lithosphere has a life cycle that begins at mid-ocean ridges and ends at subduction zones, we still do not have a clear understanding of how the continental lithosphere first formed, or why the lithosphere has remained stable over billions of years, despite undergoing significant deformation in later tectonic events. In Australia, the oldest parts of the continental lithosphere are dated to about 3.2 billion years old, making it an excellent location for testing out hypotheses related to continental formation and evolution. Detailed geologic studies over decades have placed constraints on the timing of many of Australia's major tectonic events. However, observations of seismic anisotropy, which are used to infer information about tectonic deformation, tell a story about the Australian lithosphere that is significantly more complicated than what is inferred from the surface geology. The goal of this project is to use newly developed seismological methods to provide a more detailed and accurate picture of seismic anisotropy to help infer the tectonic evolution within the Australian continent, in order to better understand the processes of continental formation, assembly and evolution more generally. The character of the anisotropic structure in the mantle lithosphere and asthenosphere beneath Australia represents a long-standing puzzle, largely because inferences gleaned from different data analysis methods (SKS splitting vs. surface wave tomography) often conflict. This proposal will apply frequency-dependent SKS splitting analysis and anisotropic Ps receiver function analysis to place more precise constraints on the lateral and depth variability of anisotropy beneath the Australian continent. The proposed work has three specific goals: 1) Use data from 26 permanent broadband stations to measure frequency-dependent SKS splitting and apply Ps receiver function analysis, and for a subset of stations, carry out detailed forward modeling of the structure and compare results across methods for a subset of these stations. 2) Investigate the origin of depth-dependent anisotropy beneath Australia by analyzing models for anisotropic structure in terms of tectonic history and setting. 3) Understand the origin of the discrepancies between azimuthally anisotropic surface wave models and SKS splitting observations beneath Australia via comparisons with the independent depth-dependent models. Some specific science questions addressed by this work include: How does anisotropy vary with depth beneath the Australian continent? Do variations in anisotropic structure correspond to geologic and/or tectonic structures? Does the anisotropic structure of the mantle lithosphere shed light on past episodes of deformation? Why have previous studies identified discrepancies between surface wave tomography models and SKS splitting observations?