Rapid Seismic and Infrasound Assessment of Large Landslides: A Case Study From Denali National Park and Preserve (Alaska)

Abstract Large, rapid landslides are a global hazard that can occur in remote, mountainous areas. Eyewitness reports of landslides and satellite imagery can often be limited or delayed, particularly during inclement weather. However, landslide‐generated seismic and infrasound (low‐frequency atmospheric sound) waves can be remotely detected in near real‐time. This information can significantly expedite characterization and possible landslide response activities. Here, we highlight these capabilities using a 6.1 million m 3 ice–rock avalanche in Denali National Park and Preserve (Alaska). This event was detected via a landslide‐specific seismic location and volume estimation algorithm deployed in Alaska, and—notably—by standard earthquake monitoring systems. Following rapid detection of this event, we combined its seismic and infrasound data set with optical, synthetic aperture radar, and oblique aerial imagery, multitemporal digital elevation models, and a numerical flow model to reconstruct its failure timeline and dynamics. We apply array processing to infrasound signals traveling >250 km and find that two precursory events occurred minutes prior to the main failure. We use long‐period seismic signals to infer the force exerted by the landslide on the Earth and constrain the rheological parameters of our numerical flow simulation with this result and deposit morphology. The main failure produced a steeply dipping impulsive initial downward force and reached speeds exceeding 60 m/s. This impulsive force generated relatively strong seismic body waves, which contributed to the earthquake system detection. This large, remote Alaska landslide underscores the key value of seismic and infrasound analysis for rapid landslide assessment and motivates efforts to further operationalize these approaches.