NSF Award
2448002
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. <br/><br/>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.<br/><br/>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.
