Developing a comprehensive model of subduction and continental accretion at Cascadia

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Cascadia is a prime site to understand subduction dynamics and continental accretion, because it has one of the youngest subducting slabs in the world and a wide range of tectonic units. A variety of scientific questions can be addressed at Cascadia: What controls the subduction zone segmentation? What is the role of water transport in the subduction zone? Where does melting occur and how does magma migrate in the mantle and crust? And how does oceanic lithosphere accrete to the continent? Paleoseismic records show that Cascadia has a history of generating ~M9 megathrust earthquakes, so research is needed to improve the assessment of seismic and tsunami hazards from megathrust earthquakes.This project develops and implements an advanced seismological method to construct a comprehensive, high-resolution velocity model of the crust and upper mantle for the entire Cascadia subduction zone. The velocity model provides a detailed structural framework and new understanding of the subduction processes. The structural correlations of a well-resolved model help address whether serpentinization of the forearc mantle varies substantially along strike and how it is related to the subduction of sediments, pre-existing features on the slab, and melt production beneath the volcanic arc. The project tests whether the recurrence of episodic tremor and slow slip events is related to properties of the overriding plate or the subducting oceanic plate. The new crustal model helps in understanding how accretion of oceanic lithosphere contributes to continental growth and subduction evolution. Accurate and high-resolution characterization of the crust and upper mantle structure is also critical to refining seismic and tsunami hazard assessment in Cascadia.