HR: 0800h
AN: S21B-0566    [Abstracts]
TI: Shear experiments of granular materials and implications for fault slip
AU: * Higashi, N
EM: higashi@hakusan.s.kanazawa-u.ac.jp
AF: Graduate School of Natural Sciences and Technology, Kanazawa University, Kakuma, Kanazawa, 920-1192, Japan
AU: Sumita, I
EM: sumita@hakusan.s.kanazawa-u.ac.jp
AF: Graduate School of Natural Sciences and Technology, Kanazawa University, Kakuma, Kanazawa, 920-1192, Japan
AB: Faults are known to slip irregularly in the form of stick-slip. There are various parameters which affect this motion (e.g., particle size, shear rate). But how each of these parameters affect the motion is unclear. Recently, Anthony and Marone (2005) performed laboratory experiments to investigate how the periodicity or slip are controlled by the particle properties of fault gouge. However, particle size was not varied much and the effect of interstitial fluid was unexplored. Fluid effects are considered to be important for understanding slip in subduction zones (Obara, 2002). Here we present the results of shear experiments of dry and liquid-saturated granular materials to understand how the properties of fault gouge and the imposed shear rate control the long-term statistics of fault slip. We shear sorted glass beads using a rotating viscometer and find that they exhibit stick-slip. We characterize the temporal variation of torque measurements using several scales, and analyze their statistical properties. Under a fixed rotation rate we find that as the particle size increases, the stress drop and the slip recurrence interval increases whereas the degree of creeping prior to the slip decreases. From analyzing the images of the upper surface of sheared granular materials, we find that the radial range where particles are mobile are approximately scaled as 10-15 particle size, and hence the number of particles consisting a force chain is approximately constant. Using these results, we calculate the minimum shear strain needed for a slip to occur and find that for a particle size of 0.196 mm it is 5 × 10^-3 for a shear rate of 1 × 10^-2 1/s and tends to decrease with increasing particle size. Our results indicate that the difference in the stick-slip behavior primarily arise from the difference in interparticle friction which increases with particle size. When the granular material is saturated with viscous fluid, we find that the interparticle friction is drastically reduced thus affecting the stress drop and degree of preslip creep. Although our granular model of fault slip is much simplified, it demonstrates that for the same far-field slip rate the difference of the effective particle size of fault gauge or the presence of interstial liquid can account for the variation of fault behavior from creeping to stick-slip.
DE: 5199 General or miscellaneous
DE: 7209 Earthquake dynamics (1242)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Seismology [S]
MN: 2007 Fall Meeting