Watching the Cryosphere Thaw: Seismic Monitoring of Permafrost Degradation Using Distributed Acoustic Sensing During a Controlled Heating Experiment

Permafrost degradation is rapidly increasing in response to a warming Arctic climate, altering landscapes and damaging critical infrastructure. Solutions for monitoring permafrost thaw dynamics are essential to understand biogeochemical feedbacks as well as to issue warnings for hazardous geotechnical conditions. We investigate the feasibility of permafrost monitoring using permanently installed fiber‐optic seismic networks. We conducted a 2‐month seismic monitoring campaign during a controlled thaw experiment using a permanent surface orbital vibrator (SOV) and a 2D‐array of distributed acoustic sensing (DAS) cables, and observed significant (15%) shear‐wave velocity (Vs) reductions and approximately 2 m depression of the permafrost table beneath the heating zone. These observations were validated by time‐lapse horizontal‐to‐vertical spectral ratio (HVSR) analysis from three co‐located broadband seismometers. The combination of SOV and DAS provided unique seismic observations for permafrost monitoring at the field scale, as well as a basis for design and development of early warning systems for permafrost thaw. Plain Language Summary Increased permafrost thaw, caused by a changing climate, is altering the landscape, increasing carbon dioxide emissions, and causing damage to critical infrastructure. In this context, long‐term monitoring of permafrost thaw processes is vital for hazard prevention and mitigation. Unfortunately, a variety of challenges exist for long‐term time‐lapse monitoring of thaw processes, especially in arctic settings with strong near‐surface rainfall and temperature cycles. To meet the need of inexpensive, rugged, and highly sensitive monitoring technology, we conducted a unique experiment in Fairbanks, Alaska using 4‐km of buried fiber‐optic cables as seismic sensors (called distributed acoustic sensing, DAS) to monitor changes while the permafrost was artificially warmed over a 2‐month period. A permanent seismic source generated seismic waves to repeatedly sample the near‐surface. Our results reveal significant reductions in shear‐wave velocity, indicating a decline in soil rigidity as it warmed, as well as deepening of the top of permafrost. These results suggest permafrost thaw monitoring using DAS may be an effective strategy to track changing arctic landscapes and predict areas of greatest thaw vulnerability. Key Points We evaluate a novel approach to seismically monitor permafrost degradation using DAS during a controlled heat