The influence of the pull-apart origin of the Vienna Basin on the high density of landslides in the adjacent Flysch sediments

We demonstrate, with examples from the Chřiby Highlands (Western Carpathian Flysch Belt, WCFB), that the fractured Flysch rocks here manifest higher landslide susceptibility than is commonly seen in comparable bedrock. The Chřiby Highlands represent the NE border of the Vienna Basin which developed from the Middle Miocene up to the Pleistocene as part of sinistral strike-slip movements. These last tectonic movements were followed by the post-thrusting phase as documented by the Pliocene and the Pleistocene sedimentation, and the presence of neotectonic faults. We mapped the landslides using digital elevation models and conducted field mapping. Information on recent sedimentation was obtained from unpublished borehole data available in the archive of the Czech Geological Survey. We determine that the NE part of the Chřiby Highlands has higher landslide density (11.85%) than the SW part (6.62%). The landslide density in the NE part is also higher than any previously published data from areas of a comparable size in the WCFB. It was not possible to detect all the landslides during field mapping because Quaternary loess covers some parts of the study area. We found three loess-covered landslides based on borehole data analysis. They are of Pleistocene age and rank among the oldest indirectly dated landslides in the entire WCFB. We conclude that Flysch rock fracturing, caused by both old (Oligocene–Lower Miocene) and neotectonic (Middle Miocene to Pleistocene) fault activities, induce deep rock weathering and consequently increased the susceptibility of flysch rock to landslides.