Abstract :
[en] Assessing the geometry and volume of mass movements is essential for the appraisal of slope stability and
for the understanding of slope failure trigger mechanisms. For the latter, we developed seismic ambient noise
measurement techniques in order to better characterize the sub-surface of ancient deep-seated landslides in
seismic regions, as in Carpathian Mountains in Romania and in the Swiss Alps.
In particular, we conducted two thorough seismological and geophysical campaigns on the landslides of
Eagle’s Lake and Varlaam, in the Buzau region, Romania. This region hosts very large and generally old (i.e. >
1000 years) mass movements with morphologies which might be due to seismically induced failure.
On both sites, we performed abundant horizontal-to-vertical noise spectral ratio (HVSR) measurements and
installed several seismic arrays. The HVSR technique, based on the analysis of three component seismic
signals, is commonly used to identify the resonance frequency of a given site. Through the installation of
seismic arrays, we analyze the dispersive properties of the surface waves. By jointly inverting the information
through a non-linear approach, we retrieve the shear-wave velocity profile beneath the arrays and identify
velocity contrasts with depth.
On Eagle’s Lake rockslide, the results have also been integrated with seismic refraction tomography profiles,
evidencing lateral contrasts in soil properties; and multichannel analysis of surface waves providing the
subsurface shear-wave velocities. At Varlaam, the extensive measurements performed over the landslide
allowed us to identify a major impedance contrast at depth highlighting the base of the failed body. We also
performed UAV flights to establish a 3D model of the investigated sites. All these investigations contributed to
estimate the landslide geometries. In addition, we also present the preliminary results for a completed survey
held in the Grison area in Swiss Alps.
This work aims, in prospect, at reconstructing the conditions and the energy needed for triggering these
landslides, in order to understand the seismic component, if applicable, in the failure process.
