| 英文摘要: | Earthquakes are among the most devastating natural disasters, in some cases causing extreme loss of life and untold damage to infrastructure. Earthquakes are the result of rapid sliding along fractures ? called faults - within Earth?s interior. The fairly regular recurrence of earthquakes stems from the interaction of the rocks that apply forces to a locked fault, and the mechanical behavior of fault rocks as they begin to slide past each other ? i.e., their frictional behavior. Existing mathematical descriptions of the frictional behavior of rock, which are employed in computer models of earthquakes, are based on estimates from experiments. It would be far better if such descriptions were based on a fundamental understanding of the underlying physics, as this would make their use in earthquake models far more reliable and potentially could lead to the ability to predict the timing of earthquakes, which is impossible presently. Incredibly, the initiation of earthquakes depends on physical and chemical processes that occur at very small scales on faults ? at micrometer- to nanometer-sized regions where fault surfaces are actually touching. This extreme range of relevant length scales ? from the kilometer to the nanometer scale - thus necessitates a multi-disciplinary approach, including experiments and computer simulations of rock friction behavior down to the nanometer scale. In this highly interdisciplinary project, tribologists, geophysicists, and materials scientists will merge their expertise to study the frictional behavior of rocks at small scales, and will integrate the knowledge of friction mechanisms thus gained with existing mathematical descriptions of rock friction to revise, if not replace, those models. The ultimate goal of the proposed work is to better understand the earthquake process, and ultimately translate that understanding to societal benefit through applications to earthquake prediction. The project will further the education of three PhD students and several undergraduates, recruited from underrepresented groups when possible. Scientific results will be incorporated into coursework, reported at materials science, engineering, and earth science meetings, and published in high impact journals across multiple disciplines.
Rate- and state-variable friction ?laws? form the basis for our limited understanding of the frictional behavior and stability of rocks in the laboratory, and are the foundation for models of earthquake nucleation and recurrence. The physical basis for these laws, however, remains incomplete to unknown, making a reliable extrapolation of them to the Earth, beyond the limited ranges of conditions explored in the experiments that form their basis, fraught with uncertainty. Incredibly, the nucleation of fault-scale slip events (earthquakes) depends on micro-to-nanoscopic physico-chemical processes that occur at frictional contacts on faults. This extreme range of relevant length scales thus necessitates a multi-disciplinary approach, including experiments and atomistic simulations of Earth materials down to the nanoscale. The goal of this project is to develop physically-based constitutive laws for the frictional behavior of rocks that can be extrapolated to the Earth with confidence. To achieve these goals, the PIs will apply a highly interdisciplinary approach that explores the physical mechanisms of rock friction over a wide range of length scales using a broad range of cutting-edge experimental methodologies, including atomic force microscopy (AFM), nanoindentation, and nanolithography. Critically, these experiments will be coupled with, and will inform and validate, atomistic simulations of the key physical processes that contribute to the frictional behavior of Earth materials. Specifically, the team will 1) Study adhesion and indentation creep of silica and quartz using AFM, in situ electron microscopy, nanoindentation, and atomistic simulations to determine the role that interfacial chemical bonding and plastic asperity creep play in frictional aging (the ?evolution effect?), 2) determine the physical mechanism underlying the ?direct effect? by extrapolating the mechanisms revealed in single-contact AFM experiments and simulations to macroscopic friction behavior of rocks via multi-contact models, and 3) use microstructural analyses and innovative nanolithographic techniques to determine the relative proportions of elastic and plastic contacts in loaded rock interfaces, and provide quantitative links between single-contact and multi-contact aging behavior. |