Seismic Structure of Central Canada at Multiple Scales

加拿大中部多尺度地震结构

• 批准号: RGPIN-2020-05350
• 负责人: Frederiksen, Andrew
• 金额: $ 2.19万
• 依托单位: University of Manitoba
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=754969
• 关键词: Seismic; Structure; Central; Canada; Multiple

The physical principles of seismology are scale independent, governing waves propagating in a few metres of soil or over distances of thousands of kilometres. However, in practice these different scales are typically examined using different approaches by different people. I propose to address this through a program that exploits scale independence, examining the large-scale structure of North America and adjacent oceans, regional-scale crust and upper-mantle structure in the midcontinent, and small-scale bedrock topography in the Red River valley. The largest-scale project I propose is a new tomographic model of the Canadian lithosphere from two-station surface-wave analysis, combining our recently published two-station data for the Cordillera with eastern-Canada data from the UQAM group. The model will be easily updated as new data are available. I also propose a new source of surface-wave data: ocean-bottom seismographs. Using data from past experiments, I will develop dispersion measurement techniques that permit use of ocean-to-shore and ocean-to-ocean paths. This will allow the Canadian model to extend offshore, examining lithosphere beneath the continental shelf and slope. The approach will be more valuable once instruments of the National Facility for Seismic Imaging begin to produce data in the next few years, and will bridge the currently separate domains of continental and marine seismology. I propose to continue work in central North America using data from the Superior Province Rifting Earthscope Experiment. Tomography has not located a major Mid-Continent Rift (MCR) related lithospheric feature, while receiver functions have found a pervasive underplated layer along the MCR axis. The lack of a mantle anomaly beneath the MCR is in contradiction with the large amount of underplated material, unless the underplate was extracted from a deeper source. I will address this gap by applying shear-wave splitting to mantle fabric along the MCR axis, to assess resetting due to rifting. I will constrain the underplate using a transfer-function technique that I developed. Better knowledge of how rifting interacted with lithosphere will aid in understanding North American tectonics and modern rifts. On a small scale, I propose to improve techniques for measuring depth to bedrock using portable seismic equipment, and test their viability in the Red River valley. Existing ambient-noise MASW methods require directional noise; I propose to adapt interferometry used at the crustal scale to recover waves from diffuse noise, which is present everywhere. Better depth-to-bedrock measurement is essential for engineering/geotechnical studies and overburden characterization. The common goal is bridging domains of seismology through scale independence, from continent to ocean and from lithospheric to crustal to near-surface, and so extending the applicability of seismic techniques while better characterizing the tectonic history of North America.

地震学的物理原理是尺度无关的，控制着波在几米厚的土壤中传播或在数千公里的距离上传播。然而，在实践中，这些不同的量表通常由不同的人使用不同的方法进行审查。我建议通过一个利用尺度独立性的计划来解决这个问题，研究北美及其邻近海洋的大尺度结构，中大陆的区域尺度地壳和上地幔结构，以及红河谷的小规模基岩地形。我建议的最大规模的项目是一个新的加拿大岩石圈层析模型，它来自两个台站的面波分析，结合了我们最近发布的科迪勒拉的两个台站数据和UQAM小组的加拿大东部数据。随着新数据的出现，该模型将很容易更新。我还提出了一种新的面波数据来源：海底地震仪。利用过去实验的数据，我将开发允许使用海洋到海岸和海洋到海洋的路径的色散测量技术。这将允许加拿大的模式延伸到近海，研究大陆架和斜坡下的岩石圈。一旦国家地震成像设施的仪器在未来几年开始产生数据，这种方法将更有价值，并将架起目前独立的大陆地震学和海洋地震学领域的桥梁。我建议使用苏必利尔省裂谷地球望远镜实验的数据继续在北美中部开展工作。层析成像没有定位到与中大陆裂谷(MCR)相关的主要岩石圈特征，而接收器功能发现了沿MCR轴线普遍存在的垫层。MCR之下缺乏地幔异常与大量底板物质相矛盾，除非底板是从更深的来源提取的。我将通过将横波分裂应用于沿MCR轴的地衣织物来解决这一差距，以评估由于裂隙而导致的重置。我将使用我开发的传递函数技术来约束底板。更好地了解裂谷作用与岩石圈的相互作用将有助于理解北美的构造和现代裂谷。在小范围内，我建议改进使用便携式地震设备测量基岩深度的技术，并在红河流域测试其可行性。现有的环境噪声MASW方法需要定向噪声；我建议调整地壳尺度上使用的干涉测量法，以从漫射噪声中恢复波，漫射噪声无处不在。更好的基岩深度测量对于工程/岩土研究和覆盖层表征是至关重要的。共同的目标是通过尺度无关性，从大陆到海洋，从岩石圈到地壳到近地表，在地震学领域之间架起桥梁，从而扩大地震技术的适用性，同时更好地描述北美的构造历史。