Permafrost Distribution and Percolating Water at Mt. Zugspitze: Insights from Seismology including DAS

Degradation of mountain permafrost due to global warming reduces the stability of steep rock slopes, increasing the hazard potential for humans and infrastructure. However, detection and continuous monitoring of permafrost environments remains challenging due to the harsh conditions typically encountered in high Alpine terrain. In this study, we present results from passive seismic monitoring conducted at Mt. Zugspitze in the German/Austrian Alps.

Between 2021 and 2023, we collected continuous passive seismic data from three small seismic arrays installed along the permafrost-affected ridge to the west of the summit. This dataset is complemented by campaign-wise distributed acoustic sensing (DAS) in the tunnel systems beneath the ridge, as well as rock temperature logging and cleft water flow measurements at multiple locations near our seismic deployments.

Coda-wave interferometry reveals seasonal seismic velocity changes for most station pairs. Regarding rock temperature, pairs including stations located on the warmer south-facing slopes are primarily influenced by seasonal freezing only, whereas station pairs located on the colder north-facing slopes also indicate active-layer deepening and thus the presence of permafrost. Additionally, slant-stack analysis of DAS recordings from the northern part of the ridge also provides evidence for active-layer development during summer and fall, offering in-situ seismic observations of permafrost dynamics. Besides rock temperatures, some station pairs show a strong correlation with water flow through rock fractures, which may influence permafrost distribution.

Compared to other methods, seismology is less laborious and costly, non-invasive and allows continuous monitoring. Here, we demonstrate that it can effectively monitor freeze-thaw processes and locate permafrost. Furthermore, the results from our northern ridge deployments show evidence for extensive active-layer thaw and refreeze, indicating that permafrost may be more wide-spread than previously suggested by other studies.