2-3D dynamic numerical modelling of seismically induced rock slope failures

The stability of rock slopes is often guided significantly by the structural geology of the rocks composing the slope. In this work, we analyse the influence of structural characteristics, and of their seismic response, on large and deep-seated rock slope failure development. The study is focused on the Tamins and Fernpass rockslides in the European Alps and on the Balta and Eagle’s Lake rockslides in the southeastern Carpathians. These case studies are compared with catastrophic rock slope failures with ascertained or very likely seismic origin in the Tien Shan Mountains. The main goal is to identify indicators for seismically induced rock slope failures based on the source zone rock structures and failure scar geometry. We present examples of failures in anti-dip slopes and along-strike rock structures that were potentially (or partially) caused by seismic triggering, and we also consider a series of mixed structural types, which are more difficult to interpret conclusively. This morpho-structural study is supported by 2D and 3D distinct element numerical models of the Balta site (with reconstructed initial mountain morphology) showing that seismic shaking typically induces deeper-seated deformation in initially ‘stable’ rock slopes. In addition, for failures partially triggered by seismic shaking, these studies can help identify the contribution of the seismic factor to slope instability. The identification of the partial seismic origin on the basis of the dynamic response of rock structures can be particularly interesting for case histories in less seismically active mountain regions (in comparison with the Andes, Tien Shan, Pamirs), such as in the European Alps and the Carpathian Mountains. 3D models were also run to simulate the full rock avalanche process, including the formation of a dam on the valley floor.