Given that clay-rich landslides may become mobilized, leading to rapid
mass movements (earthflows and debris flows), they pose critical
problems in risk management worldwide. The most widely proposed mechanism
leading to such flow-like movements is the increase in water pore
pressure in the sliding mass, generating partial or complete liquefaction.
This solid-to-liquid transition results in a dramatic reduction of
mechanical rigidity in the liquefied zones, which could be detected
by monitoring shear wave velocity variations. With this purpose in
mind, the ambient seismic noise correlation technique has been applied
to measure the variation in the seismic surface wave velocity in
the Pont Bourquin landslide (Swiss Alps). This small but active composite
earthslide-earthflow was equipped with continuously recording seismic
sensors during spring and summer 2010. An earthslide of a few thousand
cubic meters was triggered in mid-August 2010, after a rainy period.
This article shows that the seismic velocity of the sliding material,
measured from daily noise correlograms, decreased continuously and
rapidly for several days prior to the catastrophic event. From a
spectral analysis of the velocity decrease, it was possible to determine
the location of the change at the base of the sliding layer. These
results demonstrate that ambient seismic noise can be used to detect
rigidity variations before failure and could potentially be used
to predict landslides.