Abstract
SUMMARYSeismic 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.
Highlights
Surface displacements might allow geologists to estimate failure, the prediction can be biased if the surface displacements are not representative of the kinematics at larger depth
We explore the potential of ambient vibration and earthquake monitoring on the increasingly active slope instability at Brinzauls (Switzerland)
To characterize the dynamic response on the Plateau, we deployed a temporary array of 16 seismometers on 18 June 2018 and recorded 105 min of ambient vibrations (Fig. 2)
Summary
Deep-seated gravitational slope deformations can produce significant socio-economical costs due to progressive damage and resulting maintenance of engineered structures such as lifelines and buildings. Such instabilities are prone to secondary mass movements and can eventually accelerate towards catastrophic failure. To monitor a specific high-risk slope and to investigate catastrophic failure scenarios, extensive on-site surveying is indispensable. Such monitoring is usually based on measuring surface displacements, either by optical systems or radar-based technology (Loew et al 2017; Manconi et al 2018; Glueer et al 2019). Since the acceleration of rockslides is often sensitive to hydrological forcing, alternative approaches involve modeling of the acceleration based on environmental parameters, such as precipitation and pore water pressure (Fernandez-Merodo et al 2014; Vallet et al 2016)
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