Linking Surface Deformation to Slab-Mantle Flow in the Cascadia Subduction Zone through 3D Dynamic Models

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In the Pacific northwest of the U.S. the tectonic plate beneath the Pacific Ocean is sinking below the continental U.S. along the Cascadia subduction zone plate boundary. This subduction zone is known to produce giant (larger than magnitude 8.5) earthquakes and devastating tsunamis. Over the last decade several projects have collected an unprecedented amount of data in this region. These data have already given us insight into the subduction geometry and flow in Earth's mantle. The data also have generated questions about the processes needed to explain the observations. This project will make several three-dimensional, high resolution computer models of Cascadia to explore the history and evolution of deformation at the surface of the earth and its connection to forces from the mantle below over the last million years. The output of these models will be compared to a range of observations and allow us to learn how stresses (the forces behind earthquakes) are passed from the sinking plate and mantle to the continent. We will also use these models to investigate how differences in structure of the sinking plate can affect stress patterns. The project supports a postdoctoral investigator. All code developed as part of the project will be available, and improvements and modifications made to the open source code used by this project will be contributed back to the main branch of the software.This proposal aims to address the following two questions: 1) What is the relationship between slab structure and mantle flow in Cascadia? and 2) What is the relationship between mantle flow, overriding plate heterogeneity and observed crustal deformation in Cascadia? To address question one the PI will constrain whether the subducting plate is segmented into multiple slabs by comparing model results of different cases against geological and geophysical data such as seismic anisotropy and non-arc volcanism in the overriding plate. Secondly, the deep structure and dynamic link to the surface of the Juan de Fuca slab will be investigated. Thirdly, the role of absolute plate motion on the dynamics of the slab and the overriding plate will be investigated. To address the second question, the PI will look at how mechanically distinct crustal terranes partition the deformation in Cascadia. Secondly, the role of recently active faults on the observed deformation will be examined. This proposal will use state of the art high resolution 3-D numerical models of the Cascadia subduction zone to advance understanding of how stresses are transferred across the plate boundary and through the mantle in a subduction zone with young subducting lithosphere, and how these stresses lead to the observed pattern of surface deformation and contribute to seismic hazard. The models will also significantly advance understanding of the link between mechanical heterogeneity and observed deformation patterns within overriding plates.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.