Multi-hazards assessment in Türkiye following large earthquakes

The Mw 7.8 and Mw 7.5 Kahramanmaraş Earthquake Sequence (KES) of 6th of February 2023 generated one of the most complex multi-hazard disasters in modern Türkiye, triggering thousands of landslides, severe liquefaction, widespread infrastructure damage, and subsequent flooding enhanced by an atmospheric river event. While these cascading impacts highlighted the tight coupling between seismic, geomorphic and hydrometeorological processes, quantitative multi-hazard assessments for the region remain limited. In this study, we develop an integrated, scenario-based framework to evaluate future spatially compounding hazards in southeastern Türkiye over a 50-year horizon. Earthquake ground shaking is modelled using six deterministic rupture scenarios based on seismic gaps along the East Anatolian Fault Zone. These shaking fields have then been ingested into a Generalised Additive Model (GAM) with Bayesian (Integrated Nested Laplace Approximation) INLA estimation to map co-seismic landslide susceptibility across 540,000 slope units using terrain metrics, lithology, InSAR-derived pre- and post-event deformation, and PGA. Flood hazards are simulated using the FastFlood model, incorporating design storms derived from IDF-Space statistics, CMIP6-based climate projections, soil and landcover datasets and river discharge. Landslide and flood layers are spatially harmonised and combined using the TOMRAP tool to produce a regional multi-hazard susceptibility map. Results show persistent hazard hotspots where steep terrain, susceptible lithologies, and strong shaking overlap with fluvial corridors, particularly along the northern and central sectors of the study area. The 50-year flood scenario indicates widespread inundation in major valleys, with local depths exceeding 20 m in confined reaches. When combined, multi-hazard susceptibility reaches its highest levels along mountain fronts, valley margins, and areas repeatedly exposed to both strong ground motions and hydrodynamic flooding. Exposure analysis reveals that approximately 702,000 buildings and 5.0 million people fall within mapped hazard classes, including more than 118 buildings and 850 residents in the highest hazard category. Our findings demonstrate the critical role of earthquake legacy effects, hillslope preconditioning, and hydrological amplification in shaping future multi-hazard occurrence.