New Constraints on Fault Nucleation and Propagation Using Dynamic Microtomography Experiments

Experimental rock deformation research plays an important role in understanding the mechanical behavior, deformation microstructures, and physical properties of rocks and minerals. In practice, most experiments are designed to isolate a given process, limiting access to the interplay between various processes that takes place in nature. This is in part because changes in microstructure are commonly documented after an experiment has ended. The loss of information during deformation makes quantifying feedback of different mechanisms extremely challenging. However, natural processes often involve concurrent inelastic deformation mechanisms and simultaneous metamorphic or diagenetic reactions. Quantitative accessment of these processes demands better constraints of the feedback between rock deformation and the evolving rock properties and microstructures.

Recent dynamic microtomography experiments have shown great potential in characterizing the evolution of microstructure and strain distribution during fault growth at in-situ pressure and temperature conditions. Using an X-ray transparent deformation apparatus that operates at crustal stress conditions, we have imaged the process of fault nucleation and propagation in natural rocks undergoing brittle faulting.  Applying the digital volume correlation technique to time-resolved 3-dimensional microtomographic datasets, we documented the evolution of strain distribution within a deforming rock. These results elucidate how fractures open, slide, coalesce, and propagate in rock samples responding to increasing shear stress.  

Using dynamic microtomography, it is now possible to address the effect of chemo-mechanical coupling on the emergent properties of rocks by conducting deformation experiments in which several mechanisms operate simultaneously. We studied the effect of chemo-mechanical coupling on fracturing induced by hydration reaction in serpentinite. Quantitative characterization of evolving mechanical behavior and microstructure enables us to understanding the feedback between thermal load, chemical reaction rate, and mechanical failure. Dynamic microtomography provides a promising approach to link evolving mechanical behavior with evolving microstructures. New experimental constraints on microstructural and internal stress-strain evolution can lead to more robust extrapolations of laboratory results to large scale geologic processes.