Kinematics of earthflows in the Northern California Coast Ranges using satellite interferometry

- We detect and characterize up to 50 earthflows along the Eel River using InSAR.
- We develop novel InSAR processing methods to quantify earthflow kinematics.
- We observe synchronous seasonal movement along the body of individual earthflows.
- Earthflows appear to have an irregular basal slip surface and basal topography.

Slow-moving landslides exhibit persistent downslope motion with variations in velocity driven by transient stress perturbations along the sliding surface. Here, we use satellite InSAR and high-resolution topographic data to identify 50 slow-moving landslides in the Northern California Coast Ranges, and monitor their seasonal kinematics over 4 years. These landslides have similar mechanical properties and are subject to the same external forcings, which allows us to explore geometrical controls on kinematics. To overcome errors associated with large deformation gradients we incorporate a deformation model in the InSAR processing that enables us to generate deformation time series. We test our novel methodology using a synthetic deformation time series, confirming our ability to resolve seasonal velocity patterns. Time series analysis of four representative landslides reveals that seasonal velocity changes are characterized by comparatively rapid acceleration and gradual deceleration. Each slide displays distinct kinematic zones with different mean velocities, although velocity changes appear to occur synchronously along the landslide body over seasonal timescales. Because these deformation patterns are sensitive to subsurface geometry, we employ a commonly used non-Newtonian viscous flow law to infer slide thickness and find that these slides likely exhibit a highly variable thickness and an irregular (i.e. rough and non-planar) basal sliding surface. Our results suggest that slide geometry controls long-term motion, but does not strongly regulate their response to seasonal stress perturbations.