SCEC Award Number 14018 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Angularity, Fragmentation, Heating, and Localization-- Strengthening and Weakening in Granular Fault Gouge
Investigator(s)
Name Organization
Jean Carlson University of California, Santa Barbara
Other Participants Charles Lieou, Ahmed Elbanna, James Langer
SCEC Priorities 3c, 3e, 4b SCEC Groups FARM, USR, SDOT
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 We describe plans to interpret laboratory experiments and seismological observations involving granular fault gouge, as well as to make 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 three mechanisms that occur in shear flow – porosity, comminution, and thermally induced material variations. Each of these is of interest to the SCEC Fault and Rock Mechanics community and each 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.
Intellectual Merit This project contributes to the long term goal of developing a complete, physics-based approach to constitutive laws as an intermediate between microscopic dynamics and their ultimate implications for larger scale phenomena such as stick-slip instabilities, transient overshoots, and dynamic rupture. Our focus this year was to developing quantitative fits to experimental data on fault gouge.
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.
Funds from the project were used to support the training and education of graduate student Charles Lieou at UCSB, who is expected to complete his PhD June, 2015. We also continue our collaboration with Professor Ahmed Elbanna, who has recently begun as an Assistant Professor at University if Illinois in Champaign-Urbanna.
Exemplary Figure Figure 1: Comparison of our theoretical predictions (lines) and experimental measurements (points with bars representing variance in the measurements) from van der Elst (2102) for autoacoustic compaction. Results for the normalized volume versus the dimensionless shear rate show excellent agreement between our theory and the experimental measurements. From:
Lieou, C. K. C., A. E. Elbanna, J. S. Langer, and J. M. Carlson (2014), Shear flow of angular grains: Acoustic effects and nonmonotonic rate dependence of volume. Physical Review E, 90(3), 032204. DOI: http://dx.doi.org/10.1103/PhysRevE.90.032204