Seismic Tomography Models for Alaska: Validation, Iteration, and Complex Anisotropy

阿拉斯加地震层析成像模型：验证、迭代和复杂各向异性

• 批准号: 2342129
• 负责人: Carl Tape
• 金额: $ 45.48万
• 依托单位: University of Alaska Fairbanks Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-02-01 至 2026-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2342129&HistoricalAwards=false
• 关键词: Seismic; Tomography; Models; Alaska; Validation

Seismology provides the best opportunity to investigate the interior structure of Earth. Seismometers at the Earth's surface record seismic waves from local and distant earthquakes, and these recordings can be used to derive three-dimensional images of the Earth's interior, from its innermost solid iron core to the surface. Creating these seismic images requires recordings from real earthquakes and from simulated earthquakes that calculate how waves propagate through realistic three-dimensional models of Earth's structure. By comparing real recordings with simulated recordings, it is possible to improve the models of Earth's structure. In this project, these simulations of seismic waves will be used to investigate previously established models of the subsurface structure of Alaska, as well as to develop new models based on recently recorded earthquakes. The results will enable a better understanding of the relationship between earthquakes and faulting in Alaska, while providing a more accurate method for determining the places where certain ground motion is expected to be relatively strong due to the presence of sedimentary layers at the Earth's surface. The project will establish general procedures for other scientists to interrogate Earth structure models made by other methods and data sets. The project promotes free and open software development and training opportunities, and it advances two topics relevant to society—computational science and elasticity—with potential benefits to seismic hazard assessments, oil and gas seismic imaging, materials science, and structural engineering.Seismic images of Earth's interior structure, also known as tomographic models, are commonly produced by approximate methods, and they are typically qualitatively compared to one another. These images and comparisons raise fundamental questions regarding the accuracy of the images as well as how to interpret them in the context of the compositional and thermal structure and dynamics of the Earth. This project addresses three facets of this problem. First, it will use seismic wavefield simulations to generate the simulated seismograms needed for comparison with the recorded seismograms. This will enable the most accurate physics to be deployed within the imaging problem. Second, it will apply wavefield simulations to a reference data set to directly and fairly compare previously derived tomographic models. Third, it will formalize these procedures and offer them to others by hosting a virtual workshop featuring how to access tomographic models from the Earth Model Collaboration and how to perform seismic wavefield simulations in the open-source software package Specfem3D. The focus of these efforts in on Alaska, which has had exceptional coverage of EarthScope seismic stations since 2017 and exhibits extreme subsurface tectonic complexity caused by collision at the eastern margin of the Aleutian-Alaska subduction zone. The availability of earthquakes, the quality of station coverage, the complexity of subsurface structure, and the complexity of subsurface geodynamics all provide motivation for using Alaska as a focus for the broader effort of validating and improving tomographic models. The efforts will consider a more complex representation of Earth structure, in the form of tilted transverse isotropy, which is present in minerals and rocks (for example, shale) but which is challenging to determine at larger scales, such as the crust and uppermost mantle.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.

地震学提供了研究地球室内结构的最佳机会。地球表面记录地震波的地震仪来自局部和不同的地震，这些记录可用于从其最内向的固体铁芯到表面来得出地球内部的三维图像。创建这些地震图像需要从真实地震和模拟地震中进行记录，这些地震是通过地球结构的现实三维模型来计算波浪如何传播的。通过将真实记录与模拟记录进行比较，可以改善地球结构的模型。在该项目中，这些对地震波的模拟将用于研究阿拉斯加地下结构的先前建立的模型，以及基于最近记录的地震开发新模型。结果将使阿拉斯加地震与断层之间的关系有了更好的了解，同时提供了一种更准确的方法来确定由于地球表面上存在沉积层，预计某些地面运动相对较强。该项目将为其他科学家建立一般程序，以询问其他方法和数据集制造的地球结构模型。该项目促进了自由和开放的软件开发和培训机会，并在两个与社会相关的主题（汇编科学和弹性）中推进了两个主题，以及对地震危险评估，石油和天然气地震成像，材料科学和结构工程的潜在好处。地球的内部结构（同样是典型的方法），它们通常是典型的，并且是典型的一部分。这些图像和比较提出了有关图像准确性的基本问题，以及如何在地球的组成和热结构和动力学的背景下解释它们。该项目解决了此问题的三个方面。首先，它将使用地震波场模拟生成与记录的地震图进行比较所需的模拟地震图。这将使最准确的物理能够在成像问题中部署。其次，它将将波场模拟应用于参考数据集，以直接和公平地比较先前派生的层析成像模型。第三，它将通过举办一个虚拟研讨会来形式化这些程序，并将其提供给其他程序，该讲习班如何访问地球模型协作中的层析成像模型以及如何在开放源代码软件包SpecFem3D中执行地震波场模拟。这些努力的重点放在阿拉斯加（Alaska）自2017年以来对Earthscope地震站的特殊覆盖范围，并表现出是由Aleutian-Alaska俯冲带的东部边缘碰撞引起的极端地下构造复杂性。地震的可用性，车站覆盖范围的质量，地下结构的复杂性以及地下地球动力学的复杂性都为使用阿拉斯加作为验证和改进层析成绩的更广泛努力的重点提供了动力。这些努力将以倾斜的各向同性的形式考虑地球结构的更复杂的代表，这是在矿物和岩石中存在的（例如，页岩），但要在更大的规模上确定，例如地壳和上层地幔，例如NSF的法定任务，并通过评估了Intellia的支持。