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

Andrew Gase博士获得了NSF海洋科学博士后研究奖学金，利用海洋地震数据集研究沿着夏洛特女王断层（QFC）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，并与来自新墨西哥州大学的共同导师林赛沃辛顿博士合作。QCF是阿拉斯加东南部和不列颠哥伦比亚省近海约900 km长的海洋-大陆构造板块边界，可容纳太平洋和北美板块之间约5 cm/年的运动，并发生大地震。尽管了解这条断层的特征对于减轻地震灾害的重要性，但QCF的结构、性质和滑动行为却很难确定。QCF中北部附近的地震监测网络稀疏;一个新的临时海底地震仪阵列沿着断层提供了一个关键的机会，探索地震活动和机械性能。本计画将整合来自地震与人为源的地震资料，以解决下列问题：1）滑动在QCF系统中的时间与空间分布如何？断层滑动的性质在多大程度上受太平洋板块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使命，促进我们对海洋-大陆转换系统中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。除了研究的更广泛的影响，该项目将支持研究助学金的本科生在西华盛顿大学地震学，并将使PI参加为期2周的夏季研究和干本科生在新墨西哥州教育经验的讲师。QCF表现出沿走向的变化，可能会影响其地震活动性的性质，在结晶度和地壳结构。会聚角从海大沟向北逐渐减小，从10°减小到~0°，QCF的中北部被认为完全局限于一条沿着大陆-洋壳边界的狭窄的~1 km宽的断裂带。这些观测结果与滑动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影响大地震和滑动行为。该项目将评估两个假设：1）活动变形沿着QCF中北部是本地化沿着由海洋地壳和大陆地壳界定的双物质断层，和2）滑动行为是由沿断层损伤和海洋地壳结构的走向变化控制。海洋板块结构可能导致几何复杂性或影响局部滑动行为的材料特性的变化。先进的事件探测和定位技术将查明目前区域地震监测网络无法观测到的小规模地震和震群。地震层析成像利用28个宽带海底地震仪阵列记录的当地地震活动和沿QCF中北部沿着的受控源地震数据，将通过三维层析成像提供对断层带和地壳性质的无与伦比的地震速度限制。预期的结果将提供重要的限制断层属性，地壳结构，滑动行为，将告知我们的海洋大陆转换全球的理解，同时也提供了新的见解，在阿拉斯加东南部地区的地震灾害。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.