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

Andrew Gase博士被授予NSF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)沿线的地震活动和地壳结构。这项工作将在西华盛顿大学与导师艾米丽·罗兰博士和来自新墨西哥大学的共同导师林赛·沃辛顿博士合作进行。QCF是一条长约900公里的大洋-大陆板块边界，位于阿拉斯加东南部和不列颠哥伦比亚省近海，容纳了太平洋和北美板块之间约5厘米/年的运动，并发生了大地震。尽管了解这一断层的特征对于减轻地震灾害很重要，但对QCF的结构、性质和滑动行为的确定很差。青藏高原中北部附近的地震监测网很稀疏；沿断层的新的海底地震仪临时阵列为探索地震活动和力学性质提供了一个关键机会。该项目将综合来自地震和人为震源的地震数据，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)太平洋板块和北美板块的地壳结构在多大程度上控制着断层滑动的性质？这项拟议的研究将通过与美国和加拿大科学家的合作任务来推进我们对大洋-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。除了这项研究的更广泛影响外，该项目还将支持西华盛顿大学地震学本科生的研究助理奖学金，并将使PI能够作为导师参与为期两周的暑期研究和新墨西哥州本科生的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。会聚角向北从10°减小到~0°，中北部的QCf被认为完全集中在沿大陆-海洋地壳边界的一条约1公里宽的狭窄断裂带上。这些观察结果与滑移应该在较弱板块内更广泛分布的预期相冲突。同样，地壳结构和断层破坏的沿走向变化可能会影响大地震和滑动行为。该项目将评估两个假说：1)QCF中北部的活动变形位于洋壳和陆壳交界的双物质断层上，2)滑动行为受控于断层破坏和洋壳结构的沿走向变化。大洋板块结构可能会导致几何复杂性或材料性质的变化，从而影响局部滑动行为。先进的事件检测和定位技术将识别区域地震监测网目前无法观测到的小规模地震和震群。地震层析成像使用28台宽带海底地震仪阵列上记录的当地地震活动和沿青藏高原中北部的受控源地震数据，将通过三维层析成像提供对断裂带和地壳性质的无与伦比的地震速度约束。预期的结果将对断层属性、地壳结构和滑动行为提供重要的约束，这将有助于我们了解世界范围内的海洋-大陆转换，同时也为阿拉斯加东南部的区域地震灾害提供新的见解。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.