Temporal trends and controlling factors of fatal landslides in Turkey

Landslides are one of the geomorphological hazards that cause significant human, economic and natural losses worldwide and in Turkey as well. In general, landslides triggered by natural factors such as earthquakes, heavy rainfall and snow melting, or human activities cause a large number of casualties. Knowing the precise number of deaths caused by landslides and their spatial and temporal distributions will facilitate a better understanding of the losses and damages, and further to prevent and minimize the damages caused by this type of disasters. In this respect, reliable historical inventories, including past landslide events, are crucial in understanding the future landslide hazards and risks. In this study a new data set of landslides that caused loss of life in the 90-year period from 1929 and 2019 has been compiled, providing new insight into the impact of landslides for Turkey, which is Europe's topmost deadly country.

The new archive inventory indicates that in the 90-year period a total of 1343 people lost their lives across the region in 389 landslide events in Turkey between 1929 and 2019. The distribution of the fatal landslides is highly varied and concentrated in two distinct zones along the Eastern Black Sea Region and Istanbul mega-city. Our analysis suggests that on a country scale the mapped factors that best explain the observed distribution are topographic relief and gradient, annual precipitation and population density. Temporal trend analysis reveals a significant rise in the number of deadly landslides and hotspots across the studied period was observed. The detailed analysis showed that the control factors of landslides caused by different triggering mechanisms (i.e., natural and anthropogenic) also vary. The landslides of natural trigger origin are concentrated in areas with high topographic relief and slope values, whereas those triggered by anthropogenic factors are concentrated in areas with low topographic relief and slope values. While the slope values were 10.5^° in the areas where all the fatal landslides occurred, these values were 14.5^° for natural landslides and 8^° for anthropogenic landslides. In the areas where landslides triggered by natural factors, the average topographic relief is approximately 600 meters higher than the landslides of anthropogenic origin. Moreover, we observed that fatal landslides have not triggered during the seasonal rainy period, but rather caused by sudden and heavy torrential rainfall during the summer period when the average annual rainfall is low. Fatal landslides triggered by natural factors are concentrated in the Eastern Black Sea section and occur on the Upper Cretaceous and Lower-Middle Eocene volcanics classified as median volcanic rocks with an average thickness of ten meters. The landslides on these lithological units are shallow landslides, which occur mainly a few meters above the regolithic zone, where chemical weathering is severe in this area. Fatal landslides of anthropogenic origin occur in urban and metropolitan centers where human activity is high due to infrastructure and construction works, and they are predominantly corresponding with areas where the topographic relief difference is low.