Granular controls on periodicity of stick-slip events: kinematics and force-chains in an experimental fault
Abstract
While faults generally exhibit aperiodic dynamics, some generate approximately periodic earthquakes and aseismic creep events. A long-standing question is whether granular fault material such as gouge plays a major role in controlling fault dynamics such as seismicity and periodicity. In general, the resistance of granular materials to shear has two components: interparticle friction and the geometrically-limited number of ways that particles can rearrange to accommodate strain. Here, we address the importance of particle rearrangements to stick-slip dynamics through laboratory experiments in a photoelastic granular aggregate. The experiment allows the simultaneous visualization of both particle-scale kinematics and interparticle forces during shear, the latter taking the form of force chains. The stick-slip events are failures which arise in response to shearing the aggregate under a constant-volume boundary condition. Increasing the packing fraction increases the stiffness of the granular aggregate and decreases the damping during slip events. At relatively loose packing fraction, the sizes of the slip events follow an approximately power-law distribution, as opposed to an exponential size distribution at higher packing fraction. The system exhibits switching between quasi-periodic and aperiodic behavior at all packing fractions. Higher packing fractions favor quasi-periodic behavior, with a longer time interval between aperiodic events than between quasi-periodic events. This difference in the time-scale of aperiodic stick-slip deformation is reflected in both the kinematics of interparticle slip and the force-chain dynamics: all major force-chain reorganizations are associated with aperiodic events. Our experiments conceptually link observations of natural fault dynamics with current models for granular stick-slip dynamics.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.T33B2246D
- Keywords:
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- 4465 NONLINEAR GEOPHYSICS / Phase transitions;
- 8010 STRUCTURAL GEOLOGY / Fractures and faults;
- 8034 STRUCTURAL GEOLOGY / Rheology and friction of fault zones;
- 8118 TECTONOPHYSICS / Dynamics and mechanics of faulting