Collaborative Research: Statistical Physics of Fault Behavior - Dynamic Friction, Strain Localization, Comminution, Heat Transfer, and Compaction

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

Earthquakes, landslides, volcanoes, and other natural disasters are costly public reminders that geophysical processes underlying the beauty of landscapes and coastlines are also capable of massive destruction through the sudden release of stored energy. The dynamical instabilities responsible for the onset and ensuing propagation of these events are linked to fundamental physics?friction, fracture, heating, and compaction-- of granular materials subject to extreme geophysical conditions present in earthquake faults, hillsides, and volcanoes. This project aims to develop quantitative, predictive models of granular materials under stress. The physics-based approach enables the project to span scales in a manner that is inaccessible based on previous phenomenological methods. While granular materials are ubiquitous, in both nature and technology, the fundamental physics of these systems is not well understood. Development of a precise, physical description for these materials, motivated by geophysical variables and laboratory observables, will contribute to development of predictive models for natural phenomena, such as earthquakes and landslides, as well as technological processes, including granular flow, transportation, jamming, and packing, that arise in food, pharmaceutical, and construction industries. The incomplete understanding of friction, deformation, and failure in these systems limits progress in manufacturing technologies as well as forecasting natural hazards. Integrating perspectives from mechanics, statistical physics, civil engineering, and geophysics provides a wide range of scientific and educational opportunities, with impact on natural hazards policy and preparedness as well as technical training of the workforce. Central to the project is development of parallel pipelines at the sponsored institutions, aimed at broadening and supporting participation of underrepresented groups in STEM fields. Activities include K-12 outreach, collaboration with local community colleges (Santa Barbara City College and Parkland College in Champaign), and scientific, educational, and professional mentoring of undergraduate and graduate students. This project establishes a quantitative, predictive theoretical framework, based on non-equilibrium statistical thermodynamics, for modeling the influence of grain breakage, temperature variations, and grain shape on the frictional response of sheared gouge layers spanning a wide range of velocities and normal stresses. The theoretical framework is validated by quantitative fits to experimental data on sand and fault gouge obtained in the rock mechanics and geophysics communities. Target investigations include, but are not limited to the following: strain localization patterns (Riedel, boundary, Y-band) at laboratory and fault scales and partitioning of slip between these different modes; dynamics of grain breakage and its role in fault weakening and the evolution of fault zone fabric; effects of thermally-varying material properties and flash processes at the grain scale on transient and steady state frictional response; effect of grain angularity on volume changes and rheology of sheared gouge layers. The project links quantitative physical parameters to phenomenological rate-and-state laws involving porosity, temperature, pore fluid pressure, and friction. Microscopic mechanisms underlying macroscopic dynamic processes, including stick slip, and dynamic triggering will be identified.