SCEC Award Number 11111 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Multiscale Statistical Theories for Frictional Weakening and Variability in Earthquakes
Name Organization
Jean Carlson University of California, Santa Barbara James Langer University of California, Santa Barbara
Other Participants Ahmed Elbanna, Charles Lieou, Ann Hermundstad
SCEC Priorities A8, A10, A11 SCEC Groups FARM, GMP, CDM
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
We are developing a unified 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. In one project we will determine how large-scale deformation and energy flow is impacted when some internal state variable, such as the grain size in fault gouge, is changing under the influence of extremely strong driving forces. In another, related effort we incorporate the effects of broad distributions of particle sizes and energy barriers, which may be responsible for frequency dependent response and variability in friction characteristics. Our approach combines basic nonequilibrium statistical physics with the methods of engineering systems analysis, and evaluates the impact for earthquakes using large scale dynamic rupture simulations.
Intellectual Merit 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 are extending Shear Transformation Zone (STZ) theory to include three new features, previously omitted in the model: (1) breakage of granular fault gouge, (2) the dependence of material properties on the temperature, and (3) reformulating the STZ theory in the perfectly hard sphere limit. These new features are expected to be important to earthquake physics at multiple scales. Our work addresses 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.
Broader Impacts The projects were carried out and contributed to the education of Postdoc Ahmed Elbanna, and graduate students Charles Lieou and Ann Hermundstad under the supervision of Carlson and Langer. Carlson's group is diverse, and actively involved in numerous aspects of K-12 outreach and education, aimed at increasing diversity and the representation of women in the physical and natural sciences.

Our incomplete understanding of friction, deformation, and failure is a primary limiting factor in understand seismic hazards. The work accomplished here will contribute to models for seismic hazard estimation and predictive models for performance of structural materials.
Exemplary Figure Figure 1