HR: 0830h
AN: NG41B-0063    [PDF]
TI: Numerical insights into 3-D microprocesses responsible for macroscopic granular shear
AU: Hazzard, J F
EM: j.hazzard@utoronto.ca
AF: Lassonde Institute, University of Toronto, Room 119, 170 College St., Toronto, ON M5S 3E3 Canada
AU: * Mair, K
EM: k.mair@utoronto.ca
AF: Lassonde Institute, University of Toronto, Room 119, 170 College St., Toronto, ON M5S 3E3 Canada
AU: Young, P
EM: paul.young@utoronto.ca
AF: Lassonde Institute, University of Toronto, Room 119, 170 College St., Toronto, ON M5S 3E3 Canada
AB: Earthquakes commonly occur on faults containing significant accumulations of gouge therefore investigating the processes operating in granular material under shear is extremely relevant to earthquake and fault mechanics. We present a 3-D numerical model of a granular layer subjected to shear in which grains are represented by individual spheres interacting at points of contact. The 3-D models exhibit macro friction levels notably higher than corresponding 2-D models and values that approach those of recent laboratory experiments on spherical beads. The 3-D models and laboratory studies also show much smaller fluctuations in friction than the corresponding 2-D simulations. The numerical model enables an investigation of the microprocesses that produce this observed macro behavior including visualization of grain sliding, grain rolling and the evolution of transient force chains. In 3-D, an extra dimension of grain interaction reduces the ability of the grains to accommodate strain through rolling as is observed in 2-D resulting in an increase in the mean macro friction level. It is shown that fluctuations in friction are directly related to grain reorganization normal to shear. In 3-D, these fluctuations are reduced due to significant particle motion in the third dimension, leading to a steady frictional sliding curve. Since these geometrical fluctuations are small compared with 2-D models, our 3-D simulation offers potential to investigate small amplitude but extremely important second order rate and state friction effects that fundamentally control the strength and stability of fault zones.
DE: 3210 Modeling
DE: 7209 Earthquake dynamics and mechanics
SC: Nonlinear Geophysics [NG]
MN: 2003 Fall Meeting