SUMMARY Seismic measurements on unstable rock slopes are a complementary tool to surface displacement surveys to characterize and monitor landslides. A key parameter is seismic amplification, which tends to scale with the degree of rock mass degradation. Amplification also provides a direct measure of how the wavefield is intensified during seismic loading, eventually leading to coseismic failure. Here we present the dynamic response of the fast-moving Brienz/Brinzauls rock slope instability in Switzerland (10 $ \times $ 106 to 25 $ \times $ 106 m3), which threatens settlements and infrastructure in the area. The rockslide shows strong seismic amplification at two resonant frequencies with factors of up to 11 and wavefield polarization influenced by the local fracture network orientation. We monitored the dynamic response over a period of 30 months using ambient vibrations and regional earthquake recordings. We observed a change in wavefield polarization of up to 50°, coinciding with a rotation of the relative surface displacement vector field measured by geodetic systems, highlighting the linkage between wavefield polarization and stress field (i.e. rock mass kinematics). For the analysis of secondary, relative surface displacements, we propose a singular value filtering of the displacement field to remove the principal component of landslide motion. In addition, we found increased seismic amplification values after periods of strong precipitation, providing empirical field evidence that the local precipitation history is a key parameter for assessing the hazard of earthquake-induced slope failure.

Lidar measurements and UAV photogrammetry provide high-resolution point clouds well suited for the investigation of slope deformations. Today, however, the information contained in these point clouds is rarely fully exploited. This study shows three examples of large-scale slope instabilities located in Switzerland, which are actively monitored for reasons of hazard prevention. We used point clouds acquired by terrestrial laser scanning to (1) identify differences in kinematic behaviour of individual rock compartments; (2) highlight active shear planes within the moving rock mass; (3) define the kinematic process driving the slope displacements; (4) model basal sliding planes based on the 3D surface movements of rock slides; (5) calculate exact displacement angles, (6) provide estimates on destabilised rock volumes. This information has significantly contributed to the process understanding and has thus supported decision-making in hazard management.