HR: 08:45h
AN: S31D-04    [Abstracts]
TI: Comparative Laboratory and Numerical Simulations of Shearing Granular Fault Gouge: Micromechanical Processes
AU: * Morgan, J K
EM: morganj@rice.edu
AF: Rice University, Dept of Earth Science, MS-126 6100 Main Street, Houston, TX 77005 United States
AU: Marone, C J
EM: cjm@geosc.psu.edu
AF: Pennsylvania State University, Dept of Geosciences 536 Deike Building, University Park, PA 16802 United States
AU: Guo, Y
EM: yonggui@rice.edu
AF: Rice University, Dept of Earth Science, MS-126 6100 Main Street, Houston, TX 77005 United States
AU: Anthony, J L
AF: Pennsylvania State University, Dept of Geosciences 536 Deike Building, University Park, PA 16802 United States
AU: Knuth, M W
AF: Pennsylvania State University, Dept of Geosciences 536 Deike Building, University Park, PA 16802 United States
AB: Laboratory studies of granular shear zones have provided significant insight into fault zone processes and the mechanics of earthquakes. The micromechanisms of granular deformation are more difficult to ascertain, but have been hypothesized based on known variations in boundary conditions, particle properties and geometries, and mechanical behavior. Numerical simulations using particle dynamics methods (PDM) can offer unique views into deforming granular shear zones, revealing the precise details of granular microstructures, particle interactions, and packings, which can be correlated with macroscopic mechanical behavior. Here, we describe a collaborative program of comparative laboratory and numerical experiments of granular shear using idealized materials, i.e., glass beads, glass rods or pasta, and angular sand. Both sets of experiments are carried out under similar initial and boundary conditions in a non-fracturing stress regime. Phenomenologically, the results of the two sets of experiments are very similar. Peak friction values vary as a function of particle dimensionality (1-D vs. 2-D vs. 3-D), particle angularity, particle size and size distributions, boundary roughness, and shear zone thickness. Fluctuations in shear strength during an experiment, i.e., stick-slip events, can be correlated with distinct changes in the nature, geometries, and durability of grain bridges that support the shear zone walls. Inclined grain bridges are observed to form, and to support increasing loads, during gradual increases in assemblage strength. Collapse of an individual grain bridge leads to distinct localization of strain, generating a rapidly propagating shear surface that cuts across multiple grain bridges, accounting for the sudden drop in strength. The distribution of particle sizes within an assemblage, along with boundary roughness and its periodicity, influence the rate of formation and dissipation of grain bridges, thereby controlling friction variations during shear.
DE: 7260 Theory and modeling
DE: 8010 Fractures and faults
DE: 8020 Mechanics
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting