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Abstract:
Degradation of mountain permafrost in response to global warming reduces the stability of steep rock slopes, which increases the hazard potential. However, continuous monitoring of permafrost environments remains challenging due to the harsh conditions typically encountered in high Alpine terrain. Here, we present results from passive seismic monitoring of permafrost at Mt. Zugspitze in the German/Austrian Alps. Single-station coda-wave interferometry reveals seasonal freeze-thaw cycles and permafrost degradation over the past 17 years, consistent with modeled velocity changes using temperature logs from a nearby borehole. To constrain the location of these changes, we installed three small seismic arrays along the ridge of Mt. Zugspitze in summer/fall 2021 and exploit the cable car operations at the summit as stationary noise sources for direct wave monitoring between the deployment sites. The results suggest that significant seasonal freeze-thaw cycles associated with permafrost bodies only occur in the western part of the ridge, which is also favored by thermal modeling. To further pinpoint the presence of permafrost, we repeatedly employ distributed acoustic sensing along the ridge, which allows us to sense seismic wave propagation on a meter-scale. In addition to the thermal rock properties, we find that the seismic velocity is sensitive to the presence of cleft water, which may critically contribute to the stability of rock walls. In contrast to more classical methods like borehole temperature logging and electrical resistivity monitoring, seismology combines high temporal resolution and spatial insights over comparatively large areas and thus constitutes a valuable contribution to permafrost monitoring.
