Seismic Signals Monitor Debris-Flow Erosion and Channel Elevation

Channel erosion not only amplifies debris-flow magnitude and impact but also reshapes local geomorphology. However, the destructive and infrequent nature of debris flows makes in situ monitoring of channel-bed erosion processes and flow characteristics challenging. Here, we investigate seismic signals for monitoring erosion-driven geomorphic changes, using data from 18 well-documented debris flows at Illgraben, Switzerland, between 2019 and 2023. We find that integrated seismically derived impact forces over each event correlate with channel-bed elevation changes, revealing erosion thresholds. Seismic peak frequencies correlate with absolute channel-bed elevations at seismic source regions, reflecting changes in wave propagation paths due to erosion. The correlation is evident, with peak frequency shifts exceeding 15 Hz while channel-bed elevation changes were under 4 m during the 5-year period. These findings demonstrate the capacity of seismic signals to characterize debris-flow erosion and track absolute channel-bed elevations, offering new insights into geomorphic processes.