Linking Hydrological Forcing to Seismic Sensitivity in an Unsaturated Slope Using Physics-Based Modelling

With intensifying precipitation events, landslides pose increasing environmental hazards. Unsaturated slopes are key monitoring targets due to their rapid, and sometimes severe, response to rainfall. This study investigates how hydrological changes in an unsaturated slope in Eidsvoll (Norway) influence seismic velocities through time and space using a physics-based modelling framework. Vertical effective stress and density fields from hydromechanical simulations in GeoStudio are used as inputs to the Biot-Gassmann relationship to estimate time-varying P- and S-wave velocities. These velocities are used to compute Rayleigh wave phase velocity dispersion curves and sensitivity kernels for selected days throughout a 250-day (September 2019-May 2020) simulation period. The results reveal a strong coupling between infiltration, effective stress, and seismic velocities, especially in the upper part of the unsaturated slope. Rayliegh wave sensitivity is highly frequency- and depth- dependent: high frequencies (above 60 Hz) are sensitive to near-surface changes, while lower frequencies probe deeper layers. A persistent blind zone in an intermediate high-velocity layer limits the surface waves sensitivity to certain depths, underscoring the importance of survey design and the usefulness of surface waves depending on the geologic scenario. This forward modelling approach enables identification of optimal frequency ranges and target depths, providing critical input for future field investigations. These findings contribute to the development of focused site-specific seismic monitoring strategies, including passive surveys using anthropogenic noise sources or active source MASW. By bridging hydromechanical modelling and the associated seismic response using slope-scale physical processes, this approach can support early warning systems and landslide hazard assessment under changing climate conditions.