Reflection seismic and surface wave analysis on complex heterogeneous media: the case of mount toc landslide in the vajont valley

Abstract

In the framework of the Research Strategic Project Geo-Risks "Geological and hydrological processes: monitoring, modeling and impact in the North-East Italy", a seismic reflection survey and surface waves analysis were performed on the Mt. Toc landslide in the Vajont Valley, Italy. The aim of the geophysical measurements was to obtain a 2D geophysical model of the entire landslide body down to the sliding surface depth and the characterization of rock seismic velocities. Due to the critical environment, another aim of the project was also to explore the feasibility and limitations of these geophysical tools in large landslide studies. The seismic reflection survey was conducted along two lines: L1 and L2, that are 510 and 322 m long respectively, with a - ‘Vibroseis’ - operating in the vertical mode (P wave) and vertical geophones. L1 was also acquired with - ‘Vibroseis’ - in horizontal mode (SH) and horizontal geophones. The Frequency Time Analysis of surface wave was also adopted get another independent estimation of seismic velocity profile (shear wave) of the landslide body. For the surface wave study a 250 Kg drop source was used, in order to generate low frequency excitation. The large amount of recording channels furnished an image of the subsoil for the entire landslide body down to the target depth. Results are in good agreement with the borehole data and geological interpretations. Shear and compressional wave profiles allow a comparison with rock mechanical properties to be used in future rupture and slide simulations