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Low‐ to high‐velocity frictional properties of the clay‐rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy
Author(s) -
Ferri Fabio,
Di Toro Giulio,
Hirose Takehiro,
Han Raehee,
Noda Hiroyuki,
Shimamoto Toshihiko,
Quaresimin Marino,
de Rossi Nicola
Publication year - 2011
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011jb008338
Subject(s) - geology , quartz , fault gouge , mineralogy , slip (aerodynamics) , landslide , geotechnical engineering , calcite , illite , clay minerals , fault (geology) , paleontology , physics , seismology , thermodynamics
The final slip of about 450 m at about 30 m/s of the 1963 Vaiont landslide (Italy) was preceded by >3 year long creeping phase which was localized in centimeter‐thick clay‐rich layers (60–70% smectites, 20–30% calcite and quartz). Here we investigate the frictional properties of the clay‐rich layers under similar deformation conditions as during the landslide: 1–5 MPa normal stress, 2 × 10 −7 to 1.31 m/s slip rate and displacements up to 34 m. Experiments were performed at room humidity and wet conditions with biaxial, torsion and rotary shear apparatus. The clay‐rich gouge was velocity‐independent to velocity‐weakening in both room humidity and wet conditions. In room humidity experiments, the coefficient of friction decreased from 0.47 at v < 5.0 × 10 −5 m/s to 0.12 at 1.31 m/s. Microstructural and mineralogical analyses of the gouge after experiments indicate that the dramatic weakening results from thermo‐chemical pressurization of pore fluids (smectite decomposition to illite‐type clays) and powder lubrication. In wet experiments, the coefficient of friction decreased from 0.17 at v < 1.0 × 10 −4 m/s to 0.0 at v > 0.70 m/s: full lubrication results from the formation of a continuous water film in the gouge. The Vaiont landslide occurred under wet to saturated conditions. The unstable behavior of the landslide is explained by the velocity‐weakening behavior of the Vaiont clay‐rich gouges. The formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero, even without invoking the activation of thermal pressurization. This explains the extraordinary high velocity achieved by the slide during the final collapse.

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