Research Studies by S. Zerathe and T. Lebourg, Geoazur, UNS, Nice, France.
The work focussing on the La Marbrière slope close to the town of Grasse (South-Eastern France) aims at analyzing the role of geological heritage for large-scale gravitational movements. The slope is a part of the southern edge of the subalpine chains, marked by significant structural heritage in a sedimentary context. Preliminary observations have shown evidence of gravitational deformation characteristic of large slope movements.
A multi-scale mapping coupled with geophysical prospections shows that the gravitational deformation is controled by the inherited brittle tectonic deformation. At the surface, this control relies on spatial and geometric relationships between faults and fractures networks and gravitational morpho-structures (scarp, trench, topographic anomaly). The analysis of the gravitational morpho-structures suggests a deep anchorage of this deformation linked to large inherited strike-slip faults. The results obtained from electrical tomography profiles, that are consistent with mere modeling, allow to validate this hypothesis. The La Marbrière slope has been identified as a « deep-seated-landslide » which points out three states of gravitational slope maturation.
At the slope scale, the different stages of evolution are observed in three areas marked with different morphologies and the presence of morpho-structures proper to large deep-seated landslides, such as scarps, counter-slope scarps, trenches and open-trenches. At a small scale, trenches and open-trenches are active in two zones (zone 1, zone 2) and show potential research interests that are covered by the MASSA project, especially because of high interactions between weathering process, inherited tectonics and gravitational dynamics. Due to high hazards threatening dwellings and a main road, the two zones have been multi-monitored by the Geoazur research laboratory and the MYOTIS company since October 2009.