OCE-PRF: Structural controls on fault slip behavior and deformation at the Queen Charlotte oceanic-continental transform

Andrew Gase博士获得了美国国家科学基金会海洋科学博士后研究奖学金，利用海洋地震数据集研究夏洛特女王断层（QFC）沿线的地震活动性和地壳结构。这项工作将在西华盛顿大学进行，导师是艾米丽·罗兰博士，共同导师是新墨西哥大学的林赛·沃辛顿博士。QCF是阿拉斯加东南部和不列颠哥伦比亚省近海约900公里长的海洋-大陆构造板块边界，在太平洋和北美板块之间容纳约5厘米的年-1运动，并举办大地震。尽管了解该断层的特征对减轻地震危险很重要，但对QCF的结构、性质和滑动行为却知之甚少。QCF中北部附近的地震监测网络稀疏；沿着断层的一个新的临时海底地震仪阵列为探索地震活动性和力学特性提供了一个关键的机会。该项目将整合地震和人为源的地震数据，以解决以下问题：1)滑动在QCF系统中的时间和空间分布如何？2)断层滑动的性质在多大程度上受太平洋和北美板块地壳结构的控制？拟议的研究将通过与美国和加拿大科学家的合作任务推进我们对海洋-大陆转换系统断层滑动行为的理解，这些科学家专注于不列颠哥伦比亚省近海的相关研究目标。除了研究的广泛影响外，该项目还将为西华盛顿大学地震学本科生提供研究助理奖学金，并使PI能够以讲师的身份参与新墨西哥州本科生为期两周的暑期研究和STEM教育体验。QCF在倾角和地壳结构上表现出沿走向的变化，这可能影响其地震活动的性质。海大瓜北方向辐合角从10°减小至~0°，认为中北部QCF完全局限于沿陆-洋地壳边界的窄断裂带~1 km宽。这些观察结果与人们的预期相矛盾，即滑动应该更广泛地分布在较弱的板块内。同样，地壳结构和断层破坏的沿走向变化可能影响大地震和滑动行为。本项目将评估两个假设：1)沿QCF中北部的活动变形定位于洋壳和陆壳交界的双物质断层；2)滑动行为受断层损伤和洋壳结构沿走向变化的控制。海洋板块结构可能导致几何复杂性或材料特性的变化，从而影响局部滑移行为。先进的事件探测和定位技术将识别目前区域地震监测网络无法观测到的小震级地震和地震群。利用28个宽带海底地震仪阵列记录的当地地震活动和沿QCF中北部的可控震源地震数据进行地震层析成像，将利用三维层析成像技术对断裂带和地壳性质提供无与伦比的地震速度约束。预期的结果将对断层性质、地壳结构和滑动行为提供重要的约束，这将使我们了解全球范围内的海洋-大陆转换，同时也为阿拉斯加东南部的区域地震危险提供新的见解。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。

Dr. Andrew Gase has been awarded an NSF Ocean Sciences Postdoctoral Research Fellowship to examine seismicity and crustal structure along the Queen Charlotte Fault (QFC) with marine seismic datasets. This work will be conducted at Western Washington University with mentor Dr. Emily Roland and in collaboration with co-mentor Dr. Lindsay Worthington from the University of New Mexico. The QCF is a ~900 km-long oceanic-continental tectonic plate boundary offshore Southeast Alaska and British Columbia that accommodates ~5 cm yr-1 of motion between the Pacific and North American Plates and hosts large earthquakes. Despite the importance of understanding the characteristics of this fault for earthquake hazard mitigation, the structure, properties, and slip behavior of the QCF are poorly determined. Seismic monitoring networks near the north-central QCF are sparse; a new temporary array of seafloor seismometers along the fault provides a key opportunity to explore seismicity and mechanical properties. This project will integrate seismic data from earthquake and human-generated sources to address the questions: 1) How is slip distributed across the QCF system in time and space? and 2) To what extent is the nature of fault slip controlled by the crustal architecture of the Pacific and North American Plates? The proposed research will advance our understanding of fault slip behavior at oceanic-continental transform systems through a collaborative mission with U.S. and Canadian scientists who are focusing on related research objectives offshore British Columbia. In addition to the broader impacts of the research, this project will support research assistantships for undergraduate students in seismology at Western Washington University and will enable the PI to participate as an instructor in a 2-week long summer research and STEM education experience for undergraduate students in New Mexico. The QCF exhibits along-strike variations in obliquity and crustal structure that may influence the nature of its seismicity. Convergence angles decrease northward of Haida Gwaii from 10° to ~0° and the north-central QCF is thought to be entirely localized to a narrow ~1 km-wide fault zone along the continental-oceanic crust boundary. These observations conflict with expectations that slip should be more broadly distributed within the weaker plate. Likewise, along-strike variations in crustal structure and fault damage could affect large earthquakes and slip behavior. This project will evaluate two hypotheses: 1) Active deformation along the north-central QCF is localized along a bimaterial fault bounded by oceanic crust and continental crust, and 2) Slip behavior is controlled by along-strike variations in fault damage and oceanic crustal structure. Oceanic plate structures may contribute geometric complexity or variations in material properties that influence local slip behavior. Advanced event detection and location techniques will identify small magnitude earthquakes and swarms that are not currently observable with regional seismic monitoring networks. Seismic tomography using local seismicity recorded on an array of 28 broadband ocean-bottom seismometers and controlled-source seismic data along the north-central QCF will provide unparalleled seismic velocity constraints on fault-zone and crustal properties with three-dimensional tomography. The expected results will provide important constraints on fault properties, crustal structure, and slip behavior that will inform our understanding of oceanic-continental transforms worldwide while also providing new insights into regional earthquake hazards in Southeast Alaska.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.