Do Earthquakes Wake More Slopes Than They Calm?

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 due to limited observational coverage and the masking effects of long-wavelength post-seismic signals. This knowledge gap constrains our ability to assess post-seismic landslide hazards, 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 66,800sq.km of southeastern T\"urkiye in the aftermath of the February 6, 2023, Kahramanmara\c{s} earthquake sequence. We used Sentinel-1 InSAR time series spanning three years before and one year after the earthquakes and applied a convolution-based filtering method to isolate localized surface deformation from broader tectonic signals. Given the challenge of validating deformation anomalies at a regional scale without in-situ measurements, we cross-checked these locations using high-resolution optical imagery and assigned confidence levels based on observable surface features indicative of slow-moving landslides. The resulting inventories were further enriched by expert-based assessments. Our results show that the total area affected by slow-moving landslides increased from 12.36sq.km to 159.38sq.km, reflecting a more than 12-fold rise. While a substantial number of slopes were newly activated (348), others became stabilized (28) or shifted to different deformation states (20). These findings highlight the complex response of hillslopes to seismic forcing and emphasize the importance of long-term monitoring to capture the full spectrum of earthquake-induced landslide behavior.