UC San Diego

Landslides commonly occur in areas with steep topography and abundant precipitation, and can pose a significant hazard to local communities. Some of the largest known landslides occurred in Alaska, including several that caused local tsunamis. Many more landslides may have gone undetected in remote unpopulated areas due to lack of observations. In this study, we develop an integrated procedure based on seismic and geodetic observations to detect, locate, validate, and characterize landslides in Alaska. Seismic observations have shown promise in continuously monitoring landslide occurrence, while remote sensing techniques are well suited for verification and high-resolution imaging of the detected landslides. We validate our procedure using data from the previously detected June 28, 2016, Lamplugh Glacier landslide. We also present observations of a previously unknown landslide that occurred on September 22, 2017 in the Wrangell Mountains region. The Wrangell Mountains landslide generated a coherent surface wavefield recorded across Alaska and the contiguous US. We used Sentinel-1 Synthetic Aperture Radar and Sentinel-2 optical imagery to map the respective mass deposit. To investigate the landslide dynamics, we inverted regional seismic surface wave data for a centroid single force failure model. Our model suggests that the Wrangell Mountains landslide lasted for about 140~s and had two subevents involving at least five distinct episodes. We estimate that the landslide had displaced 3.1--13.4~million tons of rocks over a distance of 2 km. Our results suggest that combining seismic and geodetic observations can vastly improve the detection and characterization of landslides in remote areas in Alaska and elsewhere, and providing new insights into the landslide dynamics.