SCEC Award Number 16135 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Dynamic friction in sheared fault gouge: implications of acoustic vibration on triggering and slow slip
Name Organization
Jean Carlson University of California, Santa Barbara
Other Participants Eric Jones, Ahmed Elbanna, Charles Lieou, James Langer, Behrooz Ferdowsi, David Goldsby, Chris Marone, Emily Brodsky, Paul Johnson
SCEC Priorities 3c, 3e, 4b SCEC Groups EEII, EFP, FARM
Report Due Date 03/15/2017 Date Report Submitted 08/15/2017
Project Abstract
The scientific objective of this project is to establish a theoretical framework, based on principles of non-equilibrium statistical thermodynamics, for modeling the influence of grain breakage, temperature variations and grain shape on the frictional response of sheared gouge layers at a wide range of velocities and normal stresses. The theoretical framework is validated by developing quantitative fits to experimental data on sand and fault gouge obtained in the rock mechanics community. This enables the investigators to extrapolate their predictions to geophysically-relevant regimes that are presently beyond reach of laboratory experiments, thereby offering experimentalists and field workers insights on what features to explore in their future work. The ultimate goal is to develop a physics-based approach to constitutive laws to bridge the gap between microscopic dynamics and large-scale phenomena such as stick-slip instabilities and dynamic rupture. The dynamic rupture models thus developed will possess a predictive capability that the classical phenomenological approaches are currently lacking.
Intellectual Merit Our results are expected to make an impact on seismic hazard estimation through development of physical constitutive laws for the fault zone, and evaluating their impact on rupture dynamics, faulting, and energy balance. More generally, our results connect the microscopic physics to macroscopic dynamics, and thus produce useful information about a variety of granular and other phenomena involving dynamics of heterogeneous materials, including rupture and slip along earthquake faults, the remote triggering of instabilities, control of friction in material processing, and fracture and toughness in composites and bio- and bio-inspired materials.
Broader Impacts This project supported the research of Graduate Student Charles Lieou, who completed his PhD in 2015. Dr. Lieou accepted a postdoctoral research position at Los Alamos National Laboratories which began in September, 2015, and continued as a collaborator on this project during this reporting period. The project supports training of graduate student, Eric Jones, who began the PhD program at UCSB in the fall of 2015, and Chantal Nguyen, who began the PhD program in fall of 2013 and began work on this project in fall 2016. The project also supports the work of an undergraduate intern, Avik Mondal, who is employed as a summer research assistant during the summers, and plans to continue research and complete an Undergraduate Honors Thesis during the academic year. This project also supports undergraduate research projects, involving field studies, statistical analysis, and laboratory investigation of field samples, of Carl Swindle and Parker Shankin-Clarke who are STEM Transfer students at Santa Barbara City College. Swindle successfully transferred to UCSB in Fall 2016.

Carlson's group is actively involved in design and implementation of several activities aimed at K-12 outreach and promotion and support of diversity in STEM fields. Our project team has participated in the UCSB K-12 Physics Circus Outreach Program, the UCSB Women in Physics, and the Santa Barbara City College STEM transfer program. The Physics Circus brings hands on demonstrations of scientific concepts to local classrooms. The Women in Physics group recruits and supports increasing the representation of women in science through a wide variety of professional development events, as well as outreach to schools and colleges. The STEM Transfer Program provides support for community college students to complete associate degree programs and transfer to Universities in STEM fields.
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.

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 121(3), 1483-1496 (2016).