This paper presents the results of monitoring flysch formation shear wave velocities at varying conditions of water content by seismic interferometry. Studies were conducted on a section of the active Just-Tegoborze landslide in the southern region of Poland. The landslide is intersected by the state road no. 75, which has a high traffic density. Measurements of the seismic interferometry were made on the basis of the registration of a local high-frequency noise generated mostly by passing heavy vehicles. Measurements were carried out in three series on January, March and July in 2015. Seismic noise vibration was registered using Güralp CMG-6TD broadband seismometers. One of the seismic profiles was located along a geological engineering cross-section prepared from research boreholes data. One of the main results of the work was the sections of changes of shear wave velocity. The interpreted seismic boundaries made it possible to correlate them with the lithological ones. The trough-like shape of the bedrock boundary may be an effect of weathering processes developed in the zone consisting of weak hieroglyphic beds. It is also supposed to be one of the slip surfaces. The seismic sections of shear wave velocity allowed to analyse velocity variations between three measurement series and to compare them with expected water content in colluvium deposits. The presented results of the study confirmed the utility of seismic interferometry based on ambient noise registration in evaluating the behaviour of landslides in the Carpathian flysch formation.

This study presents a comparison of data acquisition, processing and interpretation between passive seismic interferometry (SI) and active multichannel analysis of surface waves (MASW) methods, both using surface waves for estimation S-wave velocity field. Measurements have been taken in the same geological engineering conditions on Just-Tegoborze landslide on the south of Poland. This comparison study has an important meaning from landslide hazard evaluation point of view. The landslide is located in Magura Nappe in Outer (Flysch) Carpathians. SI was based on registration of local seismic noise generated by high traffic on the state road which intersects the landslide. The main processing step was cross-correlation of seismic noise between every pair of receivers. It led to obtain series of empirical Green’s functions for Rayleigh surface wave. However, in MASW method, seismic energy was released by an impact of 5 kg sledgehammer in a metal plate. Both methods included analysis of dispersion curves of Rayleigh surface wave. The inversion of picked fundamental modes was applied using genetic algorithm and resulted in 1D S-wave velocity models. The last step of interpretation included model visualization as the 2D S-wave velocity sections for studied profiles. Both MASW and SI methods allowed to estimate S-wave velocity field in Just-Tegoborze landslide subsurface. Dispersion images obtained from both methods provided similar phase velocity and frequency ranges. On S-wave velocity sections, the greater depth range was observed for SI method; however, lateral resolution was better for MASW. Slip surfaces in colluvial layer were not observed on either SI or MASW S-wave velocity sections. Only results obtained from SI allowed to distinguish probable slip surface located deeper, i.e. on the contact with less weathered flysch bedrock.