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

Bryant Chow博士被授予NSF博士后奖学金，以调查地震发生的原因。这项工作将在阿拉斯加大学费尔班克斯的指导下进行。地壳是所有人类活动发生的最外层。地壳破裂成许多构造板块，在其表面附近发生了地震、海啸和火山爆发等灾难性事件。地震通常发生在两个或两个以上的板块相遇的地方，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还不太清楚。该项目旨在确定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方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，曾经发生过M4级地震。其目标是描述地震的特征，并开发高分辨率的地壳模型，以了解构造力如何传递到板块内部。虽然阿拉斯加北方人口密度较低，但地震灾害对基础设施、环境和工业目的仍然很重要，对该地区的发展至关重要。阿拉斯加的北坡是美国主要的石油产区，阿拉斯加东北部是美国最大的国家野生动物保护区。该项目涉及到利用新颖的教学工具向阿拉斯加北方当地社区宣传地震风险和危害。 此外，Chow博士还将制作一个全面的模型目录，用于描述地震灾害。该项目建议对阿拉斯加北方进行详细的地震构造调查，以限制该地区及其周围的构造控制机制。北方阿拉斯加的特点是地震活动扩散和大规模变形远离板块边界。然而，所涉及的结构和过程还没有得到很好的理解。由于地理位置偏远，对北方阿拉斯加进行测绘和监测的困难导致了历史上的稀疏覆盖。在阿拉斯加部署EarthScope便携式阵列后，这种情况发生了变化，多年的高质量地震数据现在可用于全面研究。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公里外板块会聚的远场变形一致？（2）西阿拉斯加挤压伸展作用？这项工作将利用波形互相关技术和三维数值波形模拟，促进了解全球地球动力学过程如何塑造大陆尺度构造，并与区域变形和当地地震活动有关。地震活动性的检测和重新定位将通过地震矩张量的反演来约束断层结构和变形特征。波形模拟将用于验证现有的阿拉斯加北方层析成像模型，并用于随后的全波形层析成像，这将产生高分辨率的地壳和上地幔结构模型。环境噪声伴随层析成像将提供一个速度模型的北方阿拉斯加的分辨率为几十公里的顺序。随后的地震伴随层析成像反演将完善该模型的东北子集，导致公里尺度的分辨率。这些任务的成功将导致完善的地震目录，高分辨率的速度模型，以及对北方阿拉斯加构造过程的详细解释。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的学术价值和更广泛的影响评审标准。

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.