Use of the simultaneous seismic, GPS and meteorological monitoring for the characterization of a large unstable mountain slope in the southern French Alps

P>The presence of unstable rock slopes in the mountainous regions makes these areas particularly prone to the development of sudden dramatic events, which may cause damage and injuries. The efficient disaster management requires a good understanding of the main causes of these mass movements, such as, increased fluid pressure and seismic shaking. In order to improve our understanding of the mechanics and dynamics of the mountain slope instabilities, we developed a monitoring system based on microseismic, geodetic and meteorological measurements. The system operated in the La Clapiere rockslide in the southern French Alps. It was composed of four three-component seismological stations, four Global Positioning Systems (GPS) and three meteorological stations deployed together for a period of 4 months. This system was installed over the territory of similar to 1.5 km2 of the fractured gneissic terrain that moves at a mean velocity of about 70 cm yr-1. This passive measurement method may represent an interesting approach to the characterization of the landslides difficult to access, since it allows the use of the lighter instrumentation and easier processing tools. Our investigations were based on the H/V method to image shear wave contrasts that we correlated with slip surfaces. The analysis of the seismograms allowed us to point out a correlation between the thickness of the surface layers and the measured resonance frequencies. The results indicated that the H/V ratios are heterogeneous in the rockslide. Comparison between seismic and GPS data proved our monitoring approach to be promising for landslides characterization.