Imaging Upper-Mantle Structure under USArray using Long - Period Reflection Seismology

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This project will study the structure of the mantle below the United States at depths up to 800 kilometers (500 miles). Researchers will use data provided by the USArray project, which deployed ~2000 seismic stations across the United States over a 7-year period. Scientists will analyze records from distant earthquakes, called teleseisms, which contain seismic shear waves that reflect off layers and other features in the upper-mantle. By applying methods similar to those used by the oil industry to resolve crustal layering and oil reservoirs, this project will provide 3D images of the deep subsurface below the contiguous United States (i.e., excluding Alaska and Hawaii). The analyses should have superior resolution compared to most existing studies and will help resolve outstanding questions regarding the composition and tectonic evolution of the North American continent. The project will support a postdoctoral researcher and an undergraduate summer student from a program designed to increase the diversity of students in Earth and ocean sciences career paths.This research will image upper-mantle structure under the contiguous United States using reflection-seismology methods applied to topside S-wave reverberations recorded by USArray. Products will include new maps of the 410- and 660-km mantle discontinuities, as well as shallower regional upper-mantle reflectors seen in many areas, and reflections off the ancient subducting Farallon slab. The results should help relate Farallon subduction to current and past tectonics in the western United States and clarify the role of the lithosphere-asthenosphere boundary with respect to the deep cratonic root of North America. Improved resolution of sharp changes in upper-mantle structure will help address these and other issues regarding mantle composition and dynamics. Because these results are sensitive to the impedance contrast (seismic velocity and density), they provide a useful complement to seismic receiver-function studies, which are primarily sensitive to the S velocity jump alone. Preliminary results suggest the proposed method provides an exciting new way to probe upper-mantle structure, particularly when integrated with other models and data constraints.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.