Characterization of potential earthquake-triggered rock slope failures

In this ETHZ-funded project we analyze ambient vibrations and earthquake recordings to characterize and investigate the dynamic response of unstable rock slopes. We perform systematic measurements and interpretation of ambient vibrations at known unstable rock slopes, both with single stations and array-configurations. The eigenfrequencies, eigenmodes, directivity, and amplification of ambient vibrations are identified and compared to geotechnical investigations. The interpretation of recordings targets the estimation of the potential landslide volume and is supported by numerical modeling of seismic wave propagation in fractured media. A classification scheme based on the seismic response has been introduced, in which each class indicates specific properties of a rock instability. The two main classes found are volume-controlled sites and depth-controlled sites. The extensive database will be extended with instabilities on high-alpine permafrost locations. Moreover, both short-term and long-term monitoring is undertaken to understand the time evolution of the slope structure. Temporary monitoring stations are installed at the rock slope instabilities of Preonzo (Ticino) and Brienz (Grisons) and on a high-alpine permafrost ridge close to Gemsstock (Uri). A main goal of this monitoring is to understand the effect of weather and climate on the dynamic behavior of the rock and its stability, and to measure the slopes’ seismic response to earthquake ground motion. In a later stage of the project, the effect of earthquakes on the rock slope stability will be evaluated using numerical modelling. It will be evaluated, if ambient noise measurements can provide a direct proxy for the seismic vulnerability of rock slope instabilities. The expected results have the potential to be applied directly in hazard analysis and risk reduction measures.