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 博士获得了 NSF EAR 博士后奖学金，以研究地震为何发生的问题。这项工作将在卡尔·泰普 (Carl Tape) 博士的指导下在阿拉斯加大学费尔班克斯分校进行。地壳是人类所有活动发生的最外层外壳。地壳破裂成许多构造板块，在其表面附近经常发生地震、海啸和火山爆发等灾难性事件。地震通常发生在两个或多个板块相遇的地方，但也可能发生在远离板块边界的地方。引发这些地震的过程尚不清楚。该项目旨在描述地球地壳结构的特征，将地球深部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，该地区远离板块边界，曾发生过 M4 级地震，这一地区尚未得到充分研究。目标是描述地震特征并开发地壳高分辨率模型，以了解构造力如何远传到板块内部。尽管阿拉斯加北部的人口密度较低，但地震灾害对于基础设施、环境和工业目的仍然很重要，并且对该地区的发展至关重要。阿拉斯加的北坡是美国的主要石油产区，阿拉斯加东北部是美国最大的国家野生动物保护区的所在地。该项目涉及使用新颖的教学工具向阿拉斯加北部的当地社区进行宣传，以传达地震风险和危害。 此外，周博士还将制作一个全面的模型目录，可用于表征地震灾害。该项目提议对阿拉斯加北部进行详细的地震构造调查，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远离板块边界的弥散地震活动和大规模变形。然而，所涉及的结构和过程尚不清楚。由于地处偏远，阿拉斯加北部的测绘和监测存在困难，导致其覆盖范围历来稀疏。在阿拉斯加部署 EarthScope 可移动阵列后，这种情况发生了变化，现在可以使用多年的高质量地震数据进行全面研究。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公里外板块汇聚引起的远场变形一致？ (2)阿拉斯加西部的挤压延伸？这项工作将利用波形互相关技术和 3D 数值波形模拟，加深对全球地球动力学过程如何塑造大陆尺度构造以及如何与区域变形和局部地震活动相关的理解。地震活动的检测和重新定位之后将进行地震矩张量反演，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。环境噪声伴随断层扫描将提供阿拉斯加北部的速度模型，分辨率约为数十公里。随后的地震伴随断层扫描反演将完善该模型的东北部子集，从而产生公里级分辨率。这些任务的成功将带来精确的地震目录、高分辨率速度模型以及对阿拉斯加北部构造过程的详细解释。该项目由 EAR 博士后奖学金计划、刺激竞争性研究既定计划 (EPSCoR) 和 EAR 地球物理学计划共同资助。该奖项反映了 NSF 的法定使命，并通过评估认为值得支持。 利用基金会的智力优势和更广泛的影响审查标准。

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