The Distribution of Interseismic Locking on the Cascadia Subduction Zone Using Bayesian Methods

We use a Bayesian probabilistic framework to invert for the kinematic locking distribution on the Cascadia Subduction Zone, constrained by surface deformation data and a prior assumption of the locking pattern. Interseismic surface deformation observations include land and seafloor GNSS data, along with decades-averaged vertical rates from spirit leveling. Using a Bayesian inversion framework, we explore a range of priors, including different updip and downdip limits and along-strike heterogeneity in locking. Data corrections account for contemporary glacial isostatic adjustment and viscoelastic effects. The mean of the locking distributions suggests a highly coupled offshore zone, transitioning to creep at a depth that varies along strike, with sensitivity to the prior. The shape of the locking distributions varies along strike, with the highest means near the deformation front and in Central Oregon. Results suggest high probability of strong locking offshore and low locking deeper than 20 km depth, which can provide insight into associated hazards. This work also highlights the importance of tradeoffs among different deformation signals. We find that the combined influence of viscoelasticity and glacial isostatic adjustment is relatively small in Cascadia, on the order of a few mm/yr vertically, indicating that elastic strain accumulation dominates the contemporary crustal deformation.