Scenario-based regional landslide modeling with earthquake legacy effects

Strong earthquakes can change hillslope stability beyond the shaking period by changing the effective strength of slope materials and generating discontinuities that influence subsequent slope response. These earthquake legacy effects are rarely represented in regional landslide modeling, largely because scalable ways to estimate coseismic and post-seismic property changes are limited. Here we present a regional, physically based framework that jointly accounts for coseismic shear modulus degradation, post-seismic strength reduction, and scenario ground shaking to assess future slope stability conditions. We apply the approach to the 2023 Kahramanmaraş earthquake sequence in Türkiye using a detailed landslide inventory to define failed and stable slope units. Coseismic displacements are simulated with finite element modeling, and a displacement threshold provides a regional constraint to back-analyze shear modulus under seismic loading. We then develop empirical relationships between shear modulus, peak ground acceleration, and slope geometry for regional extrapolation. Future ground shaking is represented by six maximum credible rupture scenarios on fault segments identified as seismic gaps, and these scenarios are combined with spatially variable post-seismic strength changes. The proposed workflow provides a transferable and scalable approach for improving long-term landslide hazard assessment in tectonically active regions.