In the Cascadia Subduction zone, located in the Pacific Northwest of the United States, the Juan de Fuca plate is actively subducting beneath the North American plate, creating a complex subduction zone that is historically capable of powerful M9 earthquakes. We calculate both seismic velocity and attenuation measurements, which allows us to observe how wave seismic speed and energy loss varies in the crust and upper mantle. Jointly interpreting these measurements allows us to place constraints on the structure of the subduction zone and determine characteristics such as melt distribution and temperature variation. We also compare our results to other studies, as well as to the expected structure of the subduction zone, to help interpret our results more reliably. By more clearly understanding the structure of Cascadia, we are able to better understand the processes at work within this complex and dangerous subduction zone.