Integrating initial shear modulus (G₀) derived from seismic data with long-term deep-seated inclinometer displacements at selected Polish Outer Carpathian flysch landslides

Abstract

Landslide investigations have increasingly focused on integrating geotechnical monitoring with geophysical methods to improve the characterisation of internal slope processes and deformation mechanisms. This study presents a combined analysis of long-term deep-seated inclinometer displacements and seismic measurements conducted at selected landslides located in the Polish Outer Carpathian flysch. Two instrumented landslides were investigated using multi-year inclinometer monitoring covering periods of approximately 4–9 years, together with seismic refraction surveys. The initial shear modulus at very small strains (G₀) was derived from shear-wave velocity (Vₛ) and bulk density values calibrated using laboratory measurements, providing a quantitative indicator of subsurface stiffness variability. Vertical distributions of G₀ were compared with cumulative deep-seated displacements recorded by inclinometers, which allowed the identification of kinematic-mechanical deformation zones within the landslide bodies and their relationship to lithological and structural conditions. The results indicate that the integration of geophysical stiffness parameters with long-term inclinometer monitoring enables a more detailed delineation of zones characterised by different deformation behaviour. This approach supports the interpretation of deep-seated landslide structure in flysch terrains and provides a basis for further development of site-specific slope stability assessment and monitoring strategies.