Deep fluids effects on rupture of slow-moving giant landslides as a result of stress transfer and weakening

Thursday, 18 December 2014: 9:15 AM
Yves Guglielmi1, Frederic Cappa2, Sophie Viseur1, Cécile Baudement1 and Stephane Garambois3, (1)Aix Marseille University, Marseille Cedex 03, France, (2)GeoAzur, Valbonne, France, (3)ISTERRE, Grenoble, France
Landslides in Earth’s surface accommodate slow, aseismic slip and fast, seismic rupture influenced by fluid pressures and rock frictional properties. The study of strain partitioning in two French mega-rockslides (La Clapière and Séchilienne, estimated volumes of 60 ± 10 × 106 m3, France) provides a unique insights into this influence. Here we show that, by hydromechanical modeling, a significant part of the observed rockslide motions and seismicity may be caused by poroelastic strain in the deep part of the slope, induced by groundwater table variations. In the unstable volume near surface, calculated strain and rupture are controlled by stress transfer and friction weakening above the phreatic zone and reproduce well the high-motion zone measured by geodesy and geophysics. The key model parameters are the friction weakening and the position of groundwater level that are constrained by field hydrogeochemical and geodetic data to support the physical validity of the model. These results highlighting deep fluids major control on the rupture of superficial rock slopes are of importance for giant collapse monitoring strategies and for the understanding of the near surface strain long term pluriannual evolution under weak forcing.