H/V Technique for the Rapid Detection of Landslide Slip Surface(s): Assessment of the Optimized Measurements Spatial Distribution

The investigation of landslides and slope deformation processes may require the integration of a wide range of data types, collected using different approaches, such as geomorphological, geotechnical and geophysical surveys. Among this latter category, seismic noise method can be used to detect and better understand the geometry of landslide slip surfaces. Indeed, a slip surface may generate evident contrasts in shear wave velocity due to changes in seismic impedance, generated by the different seismic velocity and density of materials at landslide boundaries. The H/V or Nakamura method allows to have a punctual information about the depth of the main impedance contrasts, thus, by performing a spatial interpolation of an adequate number of punctual depth measures, is possible to reliably estimate the depth and geometry of the slip surfaces with good accuracy. This study is focused on the relation between the number of the employed single-station seismic noise measurements and the goodness of the resulting, inferred, slip surface(s) for landslides. The final aim is to detect, if it exists, a threshold in the number of measurements beyond which the information obtained is redundant, since the variations in terms of morphology observed in the reconstructed impedance contrast surfaces become negligible. The proposed approach was validated at Castagnola Landslide (Liguria, Italy), where direct measures of the subsoil stratigraphy were available, then applied to another case study, i.e., the Roccalbegna Landslide (Tuscany, Italy), where no direct measurements, apart from those of the shallow layer geotechnical properties, were available. The experiments carried out are a proof-of-concept of the opportunities that this approach can offer.