Linking Mantle Structure and Dynamics to the Landscape Evolution of the Cascadia Forearc

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This project aims to understand how mountain building processes near subduction zones (where tectonic plates descend into the earth) may be influenced by the physical state of the mantle hundreds of kilometers beneath the earth's surface. The focus of this study is on the Cascadia subduction zone, off the western United States, where variations in the landscape topography and anomalous regions deep in the earth have been observed. To better understand the deep structure, energy from distant earthquakes will be used to create 3D images. A goal of this project is to refine these images by incorporating multiple data types into a single coupled model. To understand the mountain building process, simulations will be run which predict how topography changes through time. Combining these methods, we can test what influence the deep earth has on how the overlaying landscape evolves.This project will investigate the mantle's influence on surface processes in the Cascadia subduction zone by synthesizing seismic data sets through joint inversions and performing numerical modeling of landscape evolution for southern Cascadia. This project will have three primary components. First, by jointly inverting teleseismic P and S data, physical properties of the subslab mantle will be constrained throughout Cascadia by investigating Vp/Vs ratios and testing the sensitivity to different data subsets and inversion parameters. Next, by testing and inverting data using three-dimensional anisotropic starting velocity models, our understanding of mantle flow will be merged with isotropic velocity structure to better constrain the 3D nature of flow and how it relates to the inferred physical state of the subslab. Finally, using a numerical landscape evolution model, this project will focus in on southern Cascadia to better constrain the timing and relative importance of uplift due to either subslab buoyancy or the migration of the Mendocino triple junction.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.