Tracking Slow-Moving Landslide Responses to the 2023 Kahramanmaraş Earthquake With InSAR

Abstract

Strong earthquakes can have a dual impact on the slow-moving landslide budget of a landscape by either triggering new actively deforming hillslopes or stabilizing existing ones. However, their regional-scale influence on hillslope processes remains poorly understood because of limited observational coverage and the masking effects of long-wavelength post-seismic signals. This knowledge gap constrains post-seismic landslide hazard assessment, particularly since actively deforming hillslopes may evolve into rapid failures, especially under the influence of meteorological factors following a major earthquake. This study addresses this gap by analyzing slope instability across approximately 66,800 km² of southeastern Türkiye following the 6 February 2023 Kahramanmaraş earthquake sequence using Sentinel-1 InSAR time series. We cross-validated these locations using high-resolution optical imagery, manually delineated and validated the polygons, and assigned confidence levels based on observable surface features indicative of slow-moving landslides. Our results show that the total area affected by slow-moving landslides increased from 12.36 km² before the earthquakes to 159.39 km² afterward, a 12.9-fold increase. We identified that newly activated slopes were primarily associated with steeper terrain across a broad range of ground shaking, whereas stabilized slopes were preferentially linked to very high shaking levels on intermediate slopes. Slopes that were already moving were largely influenced by intermediate shaking intensities and gentler topographic gradients. These results demonstrate that earthquake-induced changes in slow-moving landslides depend on both the pre-event activity state and the combination of seismic, topographic, and geological conditions.