Collaborative Research: CSEDI: Integrating Seismic Anisotropy, Mantle Flow, and Rock Deformation in Subduction Zone Settings

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Subduction zones are locations where one tectonic plate dives underneath another. They are an essential component of plate tectonics and the setting of the most hazardous earthquakes and volcanoes. Mantle flow above and below the subducting plate is driven by the motion of the subducting slab. The primary tool for investigating mantle flow at subduction zones is measuring the directional dependence of seismic wave speeds. Variations in wave speeds - called seismic anisotropy - arise from the alignment of minerals caused by mantle flow. However, this technique requires linking seismic observations to data on the alignment of mineral grains in deformed rocks, in the context of mantle flow. Here, the team combines state-of-the art rock-deformation experiments with models of mantle flow and models of seismic anisotropy in mantle rocks. They generate synthetic seismic waves that are compared with observations in Alaska, Cascadia, and South America. The overarching goal is to improve the understanding of mantle flow in subduction zones and better constrain plate tectonics. The project provides support for graduate and undergraduate students trained in a rich interdisciplinary environment. It also fosters outreach to K-12 students and teachers. The project outcomes will be shared with the community, notably through a multi-disciplinary conference on this topic. The project activities yield a holistic view of mantle flow, olivine texture development, and seismic anisotropy observations in subduction zones. The project is organized around three tasks. First, the researchers conduct a new set of high pressure and temperature olivine deformation experiments using the Large Volume Torsion (LVT) apparatus at Washington University in St. Louis. The aim is to determine how strain produces and subsequently modifies crystallographic preferred orientation (CPO). They use these results to produce a suite of experimentally validated parameters for use in the D-Rex texture modeling program, which simulates the formation and evolution of olivine CPO. Second, the updated D-Rex model is incorporated into new 3D models of subduction zones; these models use a nonlinear rheology and a set of alternative assumptions on the distribution of water in subduction zones. Third, the team uses the results of the numerically modeled subduction zones to simulate shear wave splitting in the mantle wedge and sub-slab mantle, using full-wavefield simulation techniques. Through these steps, the researchers define an ensemble of potential interpretations of mantle flow near subduction zones that are supported by existing and new data.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.