Characterizing evolution and subduction of the Juan de Fuca plate: A joint inversion of ambient noise and air-gun shot data

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Subduction zones where one of Earth?s tectonic plates is forced beneath another tectonic plate are one of the least understood regions on the planet and yet create major hazards for nearby coastlines and cities. The relatively small size of the Cascadia subduction system off the US west coast provides a unique opportunity to investigate the structure and evolution of the oceanic plate from its formation to subduction, as well as the nature of the sedimentary wedge or forearc that forms just offshore and the volcanic arc that forms on the over-riding plate. The proposed project aims to construct a 3D high-resolution velocity model from the surface through the crust into the mantle lithosphere, extending from trench to arc. Specifically, this project will focus on two scientific questions: (1) What is the structure of the oceanic plate prior to and after subduction - how does the plate structure evolve with time and how hydrated is the oceanic plate prior to subduction? (2) What are the relationships between the structure of the incoming plate and the along-strike variations in the forearc structure? A well-resolved Cascadia seismic velocity model will contribute to many geological and geophysical studies, allowing for better located earthquakes and source mechanisms. The project will support the career development of a female early-career geoscientist, who is in the process of establishing a new seismology group at UMASS-Amherst. The project will support training of undergraduate and graduate students. Research products will be integrated into ongoing public outreach and introductory classes in Earth Science. Wave propagation simulation and ground motion maps are great tools to educate the public in New England about seismic hazards. Results will be introduced to underserved 8th-12th grade girls through the Girls Inc. Eureka! Program, a strong STEM-based collaboration between Girls Inc. of Holyoke, Massachusetts and UMASS.Seismic imaging provides strong constraints on the geometry and physical properties of the subducting slab and the upper plate. The project will implement a joint 3D full-wave simulation and inversion of ambient noise and air-gun shots to achieve a model with high resolution from crust to uppermost mantle. Data from the Cascadia Initiative ocean bottom seismometers and onshore broadband and short-period seismic stations will be utilized, including air-gun shots of the two active-source seismic experiments. Accuracy of phase travel time in wave propagation simulation is sensitive to shallow structure, such as the sedimentary layers and water column, which will be taken into account in this study. The joint inversion of different types of seismic data into 3D models will provide a higher resolution of the oceanic plate with reduced model uncertainties than is possible with individual datasets. This project will produce a clear and complete picture of the incoming plate and forearc, which is essential for our understanding of the subduction process. More broadly, this project has very significant contribution to the scientific goals and outreach of the Cascadia Initiative community-based experiment.