Structural geology and geomorphology of giant rockslides in seismically active mountain regions

Abstract

The stability of rock slopes is strongly influenced by the structures of the involved geological materials. A series of structures, such as bedding, discontinuities and fractures are known factors decreasing the stability of rock slopes. Additionally, a rock slope can be subjected to several forms of gravitational displacement, erosional and/or weathering damage. Rock slope failures may be classified and described according to several factors, such as their volume, displacement mechanism or velocity. In this Master Thesis, especially very large deep-seated rock slope failure types are analysed according to their structural characteristics. This work does not study in detail the evolution of rockslides in general but will just focus on their origin; it intends to contribute to the understanding of the origin of larger rockslides by analysing the structural geology of their source zones. Therefore, three main analyses are completed: first, a structural analysis with stereographic projections of on-site measurements is combined with strike and dip estimations of layers in Google Earth® for five visited rockslides in the Tien Shan, the Romanian Carpathians and in the Alps (the Ak-kul rockslide in Kyrgyzstan, the Balta rockslide in Romania, the Fernpass rockslide in Austria, the Köfels rockslide in Austria and the Tamins rockslide in Switzerland); for the Balta and Tamins sites also a 3D visualisation of the strike and dip measurements is presented; second, a rapid structural study of another 46 rockslides distributed all over the World is purely based on observations in Google Earth Pro® and, third, numerical simulations are applied to a mountain slope made of rocks with various structures, to analyse the influence of bedding and joint inclination on ground deformation under static and dynamic conditions. The structural analysis based on the stereographic projections of measurements from the studied rockslides revealed some structural patterns hinting at the need for a large amount of energy to expulse the rock material from the source area for the Ak-kul, Balta, Fernpass and Tamins rockslides. Also, the results of the numerical simulations support the hypothesis that deep-seated rockslides are more likely induced by earthquakes than by static factors.