Integrated Geological and Geophysical Characterization of the 2024 Lernapat Landslide, Armenia: Slip-Surface Delineation and Stability Assessment

The May 2024 Lernapat landslide in northern Armenia occurred following rainfall and coincided with leakage from an irrigation pipeline. Its subsurface structure was investigated using UAV terrain analysis, four boreholes, laboratory testing, electrical resistivity tomography (ERT), multichannel analysis of surface waves (MASW), microtremor H/V (horizontal-to-vertical spectral ratio) measurements, ground-penetrating radar (GPR), and limit-equilibrium modelling. Boreholes identified mechanically weakened intervals at depths of 16.4–16.7 m and 18.4–20.0 m. The borehole observations were considered together with the ERT and MASW results to constrain the probable basal deformation zone and the adopted slip-surface geometry. H/V measurements provided supplementary spectral information; their depth estimates were treated as approximate equivalent thicknesses rather than independent confirmation of the MASW interpretation. The existing slope yielded factors of safety of 0.980 under static loading and 0.496 under pseudo-static loading at Kh = 0.16. A modelled groundwater lowering of 7.0 m increased these values to 1.214 and 0.616, respectively. Within the staged embankment-construction sequence, the calculated static factors of safety ranged from 1.372 to 1.499, whereas the corresponding pseudo-static values ranged from 0.657 to 0.689. None of the investigated stabilization scenarios reached Fs = 1.00 under pseudo-static loading at Kh = 0.16. No separate calculations were performed at Kh = 0.20. These factors of safety are conditional on the adopted model; the effects of alternative basal geometries and shear-strength parameters were not quantified. The results illustrate how the integration of geological, hydrogeological, electrical, and seismic observations can provide a field-constrained basis for evaluating groundwater sensitivity and stabilization scenarios.