SCEC Award Number 15050 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Mechanisms for Stick-Slip, Dynamic Triggering, and Acoustic Emissions in Granular Fault Gouge
Name Organization
Jean Carlson University of California, Santa Barbara
Other Participants Charles Lieou, Ahmed Elbanna, Paul Johnson, Chris Marone, James Langer, Emily Brodsky
SCEC Priorities 3c, 3e, 4b SCEC Groups FARM, CME, EFP
Report Due Date 03/15/2016 Date Report Submitted 03/12/2016
Project Abstract
In this reporting period we continued our work investigating the physics of plastic deformation and strain localization and the corresponding implications for dynamic earthquake problems. We examined the effect of microscopic properties and noise sources, such as grain shape, interparticle friction, and external vibrations, on the stability of granular flow rheology. This followed our recent analysis [Lieou et al., 2014b] where we showed that interparticle friction accounted for the non-monotonic dilatational effects in sheared gouge particles, seen in the experiments by van der Elst et al. [2012], hinting at inherent instabilities. We investigated the driving conditions under which stick-slip behavior emerges, and the shear rate regimes in which acoustic waves promote or suppress stick-slip, or remotely trigger slip events. This made direct connections to experiments and discrete element simulations by Paul Johnson, Chris Marone, and others (see, for example, Johnson et al. [2008]), which provide a platform for us to constrain our model parameters and improve the predictive power of our first-principles theory of deformation in granular gouge material. Our work addressed several SCEC priority science objectives in Fault and Rupture Mechanics (3c,3e and 4b) by developing physical constitutive laws for the fault zone, and evaluating their impact on rupture dynamics, faulting, and energy balance.
Intellectual Merit This project interprets laboratory experiments and seismological observations involving granular fault gouge, and makes predictions concerning fault motion and stress evolution, within the framework of the shear-transformation-zone (STZ) theory of local plastic rearrangements in granular hard-sphere systems [Lieou and Langer, 2012], pioneered by us and our colleague James Langer at UCSB. Our focus is on the mechanisms that cause stick-slip instabilities in sheared fault materials, widely known to account for earthquake rupture. This is of interest to the SCEC Fault and Rock Mechanics community and has become accessible theoretically based on advances in STZ theory made over the past several years. Our goal is to provide a first-principles, quantitative interpretation of the great wealth of experimental data on fault gouge that to date has been treated phenomenologically. The advantage of a physics-based approach is that it enables extrapolation from the lab to the field.
Broader Impacts The project addresses short-term objectives in Fault and Rock Mechanics (3c, 3e and 4b) by developing physical constitutive laws for the fault zone, validating them using granular simulations and laboratory experiments, and evaluating their seismological impact on rupture dynamics, faulting, and energy balance. A better understanding of friction will aid long-term objectives in Earthquake Source Physics and Ground Motion, informing models of fault system dynamics and physics-based hazard analysis. Accurate models of single ruptures and the overall seismicity of networks are essential to evaluating impacts of future seismic events on Southern California. The project supported work of graduate student, Charles Lieou, who received his PhD during this reporting period, and who is currently a joint postdoc in the Earth and Environmental Sciences Division and the Center for Nonlinear Studies at the Los Alamos National Laboratory, where he continues to be a promising and very active researcher in Dr. Paul Johnson's group in the field of earthquake source mechanics and nonlinear behavior in earth materials. Carlson and her group are active in K-12 Outreach in Santa Barbara County. Carlson is faculty mentor of the Physics Circus K-12 Outreach Program, which takes science demonstrations to local schools.
Exemplary Figure Figure 3: Including the weakening effect of increasing compactivity on yield stress, leads to stick-slip instabilities for certain ranges of parameters. Depending on the parameters, vibrations may amplify or suppress stick-slip instabilities, and may advance or delay the onset of slip. This has implications for remote triggering of seismicity and seismic hazard estimates. Dynamic friction in sheared fault gouge: implications of acoustic vibration on triggering and slow slip, Charles K. C. Lieou, Ahmed E. Elbanna, and J. M. Carlson, J. Geophys. Res.—Solid Earth (accepted for publication).