Seasonal Freeze‐Thaw Cycles and Permafrost Degradation on Mt. Zugspitze (German/Austrian Alps) Revealed by Single‐Station Seismic Monitoring

• Published in: Geophysical research letters Vol. 48; no. 18
• Main Authors: Lindner, Fabian, Wassermann, Joachim, Igel, Heiner
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.09.2021
• Subjects: ambient noise; Cable cars; Climate change; Climate change causes; Correlation; Cycles; Degradation; Electrical resistivity; Freeze-thawing; freeze‐thaw cycles; Glacier retreat; Glaciers; Imaging techniques; Infrastructure; Instrumentation; Labour; Melting; Meteorological data; Monitoring; Mountains; P-waves; Permafrost; permafrost degradation; permafrost monitoring; Permafrost thaws; Propagation velocity; Rocks; Seasonal variation; Seasonal variations; Seismic activity; Seismic data; Seismic propagation; Seismic stability; Seismic surveys; Seismic velocities; seismic velocity change; Seismic wave propagation; Seismic wave velocities; Seismic waves; Seismological data; Seismology; Soil degradation; Temperature rise; Temporal variations; Thawing; Tomography; Velocity; Wave propagation; Wave velocity; Germany
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL094659

Thawing of mountain permafrost in response to rising temperatures degrades the stability of rock walls and thereby affects infrastructure integrity in Alpine terrain. In this study, we use 15 yr of passive seismic data from a single station deployed near a known permafrost body on Mt. Zugspitze (Germany), to monitor freeze‐thaw processes. The recordings reveal a persistent cultural seismic noise source, which we utilize to compute single‐station cross‐correlations and extract relative seismic velocity changes. We find that parts of the cross‐correlations show seasonal velocity variations (≈3% peak‐to‐peak amplitude) and a long‐term velocity decrease (≈0.1%/yr). Comparison with meteorological data and a previous electrical resistivity tomography study suggests that these velocity changes are caused by freeze‐thaw cycles and by permafrost degradation, respectively. The results demonstrate the potential of passive seismology for permafrost monitoring and suggest that denser instrumentation will provide detailed spatio‐temporal insights on permafrost dynamics in future studies. Plain Language Summary Climate change causes permafrost (year‐round frozen rock) warming and thawing, which destabilizes rock slopes and thus constitutes a hazard potential. However, unlike glacier retreat, permafrost thawing cannot be directly observed from the surface and requires special imaging techniques for monitoring. Here, we use seismic waves generated by cable cars and other man‐made infrastructure to probe permafrost on Mt. Zugspitze (Germany) and track temporal changes over the past 15 yr. Results from a single seismic station show that the seismic wave propagation velocity in the rock is subject to seasonal variations (difference between late winter and late summer of up to 3%) and a long‐term decrease of roughly 0.1%/yr. As the seismic velocity is generally higher in frozen rock compared to unfrozen rock, the seasonal changes can be well explained by seasonal thaw and refreeze, and the long‐term changes by ongoing permafrost thawing. Because passive seismology is labor and cost effective compared to common techniques requiring active signal excitation, seismology constitutes a promising new approach for continuous long‐term permafrost monitoring. Key Points We use a single seismic station deployed near a permafrost body on Mt. Zugspitze (Germany) to monitor freeze‐thaw processes over 15 yr Cross‐correlations between the sensor components reveal seasonal velocity change cycles and a long‐term velocity decrease The changes are due to seasonal freeze‐thaw cycles and permafrost degradation, suggesting seismology as an effective permafrost monitoring tool