UNDERSTANDING VERTICAL DEFORMATION IN THE PACIFIC NORTHWEST USING VISCOELASTIC MODELS

The Juan de Fuca plate subducts underneath the Pacific plate offshore of the western United States and Canada at rates up to 45 mm/yr. Centuries have passed since the last megathrust earthquake along the Cascadia subduction zone, and this provides us the opportunity to study the late interseismic phase of subduction using the dense GNSS network that has been recording for decades in the Pacific Northwest.

The GNSS observations show a broad regional subsidence along the Cascade volcanic arc even after correcting for non-tectonic processes including hydrology and glacial isostatic adjustment. This subsidence cannot be explained by kinematic coupling models in an elastic half space. Therefore, we construct a viscoelastic model of the subduction to better understand the source of this broad subsidence. We examine the influence of plate thickness, deep slip on the megathrust, and a potential low-viscosity mantle wedge. Our results have implications for models of fault coupling on the megathrust and its interaction with the mantle lithosphere.