HR: 16:45h
AN: T14B-04    [Abstracts]
TI: The Role of Surface Roughness and Material Properties in Determining the Frictional Characteristics of Synthetic Granular Fault Gouge
AU: * Knuth, M W
EM: mwk129@psu.edu
AF: The Pennsylvania State University, Dept. of Geosciences, 521 Deike Building, University Park, PA 16802 United States
AU: Marone, C
EM: cjm@geosc.psu.edu
AF: The Pennsylvania State University, Dept. of Geosciences, 521 Deike Building, University Park, PA 16802 United States
AB: Understanding the mechanical properties of granular material is a central problem in deciphering the frictional characteristics of active faults. In order to isolate frictional processes in layers of granular fault gouge, experiments were designed to focus on three primary mechanisms by which particles interact: sliding, rolling, and dilation. To evaluate the effects of surface roughness and compressibility, we used rods composed of dried semolina pasta, alloy 260 brass, and hardwood dowels, with particle diameters of 1.86 mm, 1.59 mm, and 2.06 mm, respectively. By restricting particle motion to one or two dimensions, the experimental results produced can be compared directly with 2-D numerical modeling techniques. Layers sheared within a 2-D configuration involve all three styles of particle interaction. A 1-D sliding configuration allows only sliding parallel to applied shear. A rolling-only configuration was also developed, in which a layer of rods oriented perpendicular to shear is sandwiched between rods oriented parallel to shear. The pasta samples had mean friction coefficients of 0.24, 0.11, and 0.02 in the 2-D, 1-D, and rolling configurations, respectively. The brass rods had an average coefficient of 0.23, 0.15, and 0.01, respectively; and the wood samples had average coefficients of 0.18, 0.19, and 0.09, respectively. The changes in friction during each experiment corresponded to the displacement derivative of the layer thickness. Digital video taken of the experiments run in the 2-D configuration reveals the distribution of strain in the layer. Rapid reorientations of particles correspond to stress drops in the experimental record and may be related to the collapse and reformation of stress chains in the granular material. Some of these also correspond to sharp peaks in the recorded sound channel. A systematic relationship was found between the mean coefficient of friction of each granular material and the apparent strength of sliding contacts related to its surface roughness, as well a correlation between friction and the number of potential contact sliding dimensions in each sample configuration. These data provide important constraints on the fundamental parameters used in numerical models of tectonic faulting.
DE: 0540 Image processing
DE: 0545 Modeling (4255)
DE: 5194 Instruments and techniques
SC: Tectonophysics [T]
MN: Fall Meeting 2005