Passive seismic and electrical resistivity tomography monitoring of high-altitude rock masses under climate change: the Sas da Lech case study (Dolomites, BZ)

Long-term continuous ambient seismic monitoring and electrical resistivity tomography (ERT) surveys can be valuable geophysical techniques for understanding the response of unstable rock volumes to external meteorological variations. Their increasing application in glacial and periglacial mountain areas is mainly aimed at monitoring of rock glaciers and permafrost, being among the most reliable indicators of climate change due to their sensitivity to temperature variations. Mountain regions such as the Alps are expected to be particularly affected by 21st-century global warming, and the related permafrost thawing has potential impacts on slope stability, potentially increasing the likelihood of related hazards. Therefore, the importance of monitoring the Sas da Lech rock columns, in the Dolomites (Italy, BZ). In the site, after the occurrence of several landslide events, extensometers, multiparametric columns, and geophones were installed between 2023 and 2024. In addition, two ERT surveys were performed to have a more complete understanding of the geological and geomorphological conditions. In this thesis work are reported the analyses of the five months of data collected at the monitoring site, including a comparison with the nearest meteorological meteo station data. The latter was performed to identify the most controlling parameters on the thermo-mechanical behaviour of two rock columns resting on the Raibl Formation. Daily and seasonal scale reversible fluctuations were observed on seismic parameters mainly controlled by external air temperature, while rock temperature strongly influences the microseismic events occurrence. Given the observed sensitivity to temperature of the rock columns, a long-term temperature analysis was performed. It turned out that in the past thirty-four years the area experienced significant warming of 0.045 °C/year. Future projections, within RCP4.5 scenario, suggests a slightly decreasing temperature trend (2031-2100). Overall, the integrated analysis of the available data suggests a strong thermal control on the seismic response of the unstable rock columns. Indeed, temperature plays a key role in controlling both microseismicity and resonance-frequency variations. Given this observed thermal influence, and considering that the monitored columns rest on a lithology particularly sensitive to thawing and freezing cycles, their behaviour under external thermal forcing can be consistently explained through the geological characteristics of the site.