Clustering of Large Bedrock Landslides and Recurrent Slope Failure: Implications for Land Seismic Hazard Assessment of the Tien Shan - Djungaria Region

Spatial distribution of bedrock landslides in the Tien Shan - Djungaria mountain system is analyzed based on an inventory including more than 700 features, most of which are prehistoric and exceed 10 6 m 3 in volume. They often concentrate within limited areas several tens of kilometres in size, forming clusters divided by areas without or with very rare same-size slope failures. Two main types of landslide clusters are exemplified by case studies from the Chinese and Kazakh parts of this mountain system: those that have one giant feature surrounded by numerous much smaller landslides and those that include several more or less same-size features. Though no data about ages of slope failures that formed these clusters are available, in some cases simultaneity of their formation can be assumed with reasonable confidence. Besides, evidence of recurrent slope failure within these areas is presented. Considering arid climate of the region and limited glaciation, large earthquakes are the most likely trigger of such spatially and temporally localized slope failures, though additional studies are necessary to prove this assumption. In any case landslide and, likely, seismic hazard of such zones seem to be higher than that of the surrounding rockslide-free areas.