EAR-PF: Active Tectonics and Crustal Structure of Northern Alaska

EAR-PF：阿拉斯加北部的活动构造和地壳结构

• 批准号: 2052839
• 负责人: Bryant Chow
• 金额: $ 17.4万
• 依托单位: Chow, Bryant
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2023-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2052839&HistoricalAwards=false
• 关键词: EAR; PF; Active; Tectonics; Crustal

Dr. Bryant Chow has been awarded an NSF EAR Postdoctoral Fellowship to investigate the question of why earthquakes occur where they do. This work will take place at the University of Alaska Fairbanks under the mentorship of Dr. Carl Tape. The Earth’s crust is the outermost shell where all human activity takes place. Fractured into many tectonic plates, the crust hosts disastrous events, such as earthquakes, tsunamis, and volcanic eruptions, near its surface. Earthquakes typically occur where two or more plates meet, but they can also occur far from plate boundaries. The processes that cause these earthquakes are not well understood. This project seeks to characterize Earth’s crustal structure, linking deep-Earth processes with surface geological activity to explore why earthquakes occur where they do. The work will investigate plate tectonic processes and crustal structure in northern Alaska, an understudied region far from plate boundaries that has hosted M4 earthquakes. The goal is to characterize earthquakes and develop high-resolution models of the crust in order to understand how tectonic forces are transferred far into the interior of plates. Although population density in northern Alaska is low, earthquake hazard remains important for infrastructure, environmental, and industrial purposes and is critical for development in the region. Alaska’s North Slope is a major oil producing region for the United States, and northeastern Alaska is home to the largest national wildlife refuge in the country. This project involves outreach to local communities in northern Alaska using novel teaching tools to convey earthquake risks and hazards. Additionally, Dr. Chow will produce a comprehensive catalog of models that can be used for characterizing earthquake hazard. This project proposes a detailed seismotectonic investigation of northern Alaska to constrain mechanisms controlling tectonics in and around the region. Northern Alaska features diffuse seismicity and large-scale deformation far from the plate boundaries. However, the structures and processes involved are not well understood. Due to its remoteness, difficulties in mapping and monitoring of northern Alaska have resulted in historically sparse coverage. This changed following the deployment of the EarthScope Transportable Array in Alaska, with years of high-quality seismic data now available for a comprehensive study. This project involves investigation of two scientific questions: Are deformation and structure in northeastern Alaska consistent with (1) far field deformation from plate convergence 1000 km away? and (2) extrusional extension of western Alaska? This work will advance understanding of how global geodynamic processes shape continental scale tectonics and relate to regional deformation and local seismicity, using waveform cross-correlation techniques and 3D numerical waveform simulations. Detection and re-location of seismicity will be followed by inversion of seismic moment tensors to constrain fault structure and deformation characteristics. Waveform simulations will be used to validate existing tomography models of northern Alaska and for subsequent full-waveform tomography, which will result in high-resolution structural models of the crust and upper mantle. Ambient noise adjoint tomography will provide a velocity model of northern Alaska with resolution on the order of tens of km. A subsequent earthquake adjoint tomography inversion will refine a northeastern subset of this model, resulting in km scale resolutions. The success of these tasks will lead to refined earthquake catalogs, high resolution velocity models, and detailed interpretations of tectonic processes for northern Alaska.This project is jointly funded by the EAR Postdoctoral Fellowship program, the Established Program to Stimulate Competitive Research (EPSCoR), and the EAR Geophysics program.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.

Bryant Chow博士被授予NSF EAR博士后奖学金，研究地震发生的原因。这项工作将在阿拉斯加费尔班克斯大学进行，由Carl Tape博士指导。地壳是最外层，所有的人类活动都在这里进行。地壳分裂成许多构造板块，在其表面附近经常发生灾难性事件，如地震、海啸和火山爆发。地震通常发生在两个或多个板块相交的地方，但也可能发生在远离板块边界的地方。引起这些地震的过程尚不清楚。该项目旨在描述地球的地壳结构，将地球深处的过程与地表地质活动联系起来，以探索地震发生的原因。这项工作将调查阿拉斯加北部的板块构造过程和地壳结构，这是一个远离板块边界的未被充分研究的地区，曾发生过M4地震。其目标是描述地震的特征，并开发地壳的高分辨率模型，以便了解构造力是如何转移到板块内部的。尽管阿拉斯加北部的人口密度很低，但地震灾害对基础设施、环境和工业用途仍然很重要，对该地区的发展至关重要。阿拉斯加的北坡是美国的主要产油区，阿拉斯加东北部是美国最大的国家野生动物保护区。这个项目涉及到阿拉斯加北部的当地社区，使用新颖的教学工具来传达地震的风险和危害。此外，周博士将制作一份全面的模型目录，可用于描述地震危险。该项目提出了一项详细的阿拉斯加北部地震构造调查，以约束控制该地区及其周围构造的机制。阿拉斯加北部的特点是分散的地震活动和远离板块边界的大规模变形。然而，所涉及的结构和过程尚未得到很好的理解。由于地处偏远，阿拉斯加州北部在测绘和监测方面的困难导致了历史上的稀疏覆盖。随着EarthScope可移动阵列在阿拉斯加的部署，这种情况发生了变化，多年来的高质量地震数据现在可以用于全面研究。该项目涉及两个科学问题的调查：阿拉斯加东北部的变形和结构是否与(1)1000公里外板块汇聚产生的远场变形一致？(2)阿拉斯加西部的挤压延伸？这项工作将促进对全球地球动力学过程如何塑造大陆尺度构造的理解，并与区域变形和局部地震活动有关，使用波形互相关技术和三维数值波形模拟。地震活动性的检测和重新定位之后，将进行地震矩张量的反演，以约束断层结构和变形特征。波形模拟将用于验证阿拉斯加北部现有的层析成像模型，以及随后的全波形层析成像，这将产生地壳和上地幔的高分辨率结构模型。环境噪声伴随层析成像将提供分辨率为数十公里的阿拉斯加北部速度模型，随后的地震伴随层析成像反演将改进该模型的东北部子集，从而获得千米尺度的分辨率。这些任务的成功将导致精确的地震目录，高分辨率的速度模型，以及对阿拉斯加北部构造过程的详细解释。本项目由EAR博士后奖学金计划、刺激竞争性研究的既定计划（EPSCoR）和EAR地球物理计划共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Strong Upper‐Plate Heterogeneity at the Hikurangi Subduction Margin (North Island, New Zealand) Imaged by Adjoint Tomography

• DOI: 10.1029/2021jb022865
• 发表时间: 2022-01
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: B. Chow;Y. Kaneko;C. Tape;R. Modrak;N. Mortimer;Stephen Bannister;John Townend

Evidence for Deeply Subducted Lower‐Plate Seamounts at the Hikurangi Subduction Margin: Implications for Seismic and Aseismic Behavior

• DOI: 10.1029/2021jb022866
• 发表时间: 2021-07
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: B. Chow;Y. Kaneko;John Townend