The Impact of Anthropogenic Activities on the Distribution of Urban Landslides in Istanbul Megacity

As a megacity, Istanbul has been a regional center of attraction in terms of its historical, cultural, and economic importance from past to present. In terms of this feature, it has continuously received migration and expanded its urban area due to the increasing population. Rapid urbanization has brought an urban growth model with low resilience to natural hazards. In this city, which is expected to face a major earthquake in the near future, the distribution of landslides has not been focused on covering the entire urban area. In order to make the city resilient in terms of current hazards and secondary hazards after a possible earthquake, different geoscience projects were initiated by Istanbul Metropolitan Municipality in 2022. In this context, we conducted a detailed landslide assessment for the entire city of Istanbul using Digital Elevation Models (DEMs) derived from LiDAR, multi-temporal optical stereo-photo derived, and satellite imageries covering the period between 2013 and 2023. In total, 20,537 individual landslides were identified and mapped in the entire city area from the airborne LiDAR data and multi-temporal aerial photos. In order to determine the change in the distribution of landslides we prepared multi-temporal landslide inventories using multi-temporal optical aerial photographs and satellite images between 2013 and 2023. In this respect, we found that 3241 landslides were excavated, and 468 new landslides were triggered due to anthropogenic activities such as infrastructure, road construction, mining, airport construction, urban parks, and new settlement areas. We also revealed that the legacy effect in paleo-landslide complexes plays a vital role in the reactivation of many deep-seated landslides. Many of these landslides were also reactivated due to construction and infrastructure problems. In this context, we have revealed that anthropogenic impacts are the most important parameter on the current distribution dynamics of urban landslides in Istanbul. We conclude our study by highlighting that this new and comprehensive landslide inventory prepared for the megacity of Istanbul will contribute to determining landslide avoidance zones for planning new settlements and industrial areas.