EAR-PF: Investigating the role of the lithosphere-asthenosphere boundary through a 3D anisotropic velocity model of the Juan de Fuca plate

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Dr. William Hawley has been granted an NSF EAR postdoctoral fellowship to carry out research and educational plans at the Lamont-Doherty Earth Observatory of Columbia University. Plate tectonics is, in large measure, how we understand the long-term evolution of the planet Earth, and could play a role in making Earth habitable for life. Despite its fundamental importance, a precise physical description of what drives the motion of the plates remains unclear. A key component of understanding the driving forces is the region at the base of the plates, where they come into contact with the convecting mantle underneath. The PI will use seismic data from the ocean floor off the coast of the Pacific Northwest to help to characterize the structure of this critical zone beneath the plates. By inferring how seismic waves pass through the mantle, and comparing that structure with the motions of the plates on the surface, Dr. Hawley will shed light on the physics and chemistry of these interacting parts of the Earth, and will help refine our description of plate tectonics. The education plan involves outreach to schools and community organizations in and around New York City, mentoring graduate students at the Lamont-Doherty Earth Observatory, and organizing a reading group on issues related to plate tectonics. Data from two of the largest ocean bottom seismometer arrays, the Cascadia Initiative and the Blanco Transform Experiment, will be used to develop a 3D anisotropic velocity model of the oceanic mantle off the Pacific Northwest of North America. This project will combine the sensitivity of S-to-P receiver functions to strong gradients in seismic velocity and the sensitivity of Rayleigh waves to absolute seismic velocity to create a shear-wave velocity model. This isotropic velocity model will be the starting point to an investigation of the azimuthal dependence of Rayleigh wave phase velocities, resulting in a 3D model of anisotropy in the mantle. Dr. Hawley will then infer mantle flow from this anisotropic field, and compare that flow with plate kinematics on the surface, to ultimately refine the scale dependence of plate size on lithosphere-asthenosphere coupling.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.