Numerical analysis of deep-seated mass movements in the Magura Nappe; Flysch Belt of the Western Carpathians (Czech Republic)

Abstract. Deep-seated slope failures are common features in the mountains of the Raca Unit, Magura Nappe of the Flysch Belt of Western Carpathians. Since they represent very complicated system, understanding of their evolution and triggers still remains unclear. We tried to provide a back-analysis of their development by using a finite difference code (FDM) of continua (Flac 4.0). We confirmed that such large mass movements could be triggered by water saturation of the bedrock in the three particular geological and geomorphic settings. Such situation could have been caused by heavy rainfalls in humid phases of the Holocene or permafrost melting in Late Glacial. The effects of faulting, very deep weathering of the bedrock, low geotechnical parameters of smectite-rich material and the local slope geometry have also been accounted for in numerical models, as well as the other triggering factors of slope instability. FDM modelled shear zones are in agreement with observations.