Rheology of Geomaterials, Bridging Micro and Macro

Earth and some other celestial bodies in our solar system are continuously deforming. Plate tectonics, the largest expression of such deformations, is key for life on Earth as it recycles resources and nutrients throughout the crust and mantle; but is also the reason behind the majority of geological processes including natural hazards such as earthquakes, volcanic eruptions and landslides. Plate tectonics on Earth and possibly on other celestial bodies is just the visible expression of deformation occurring throughout the entire subsurface. Such deformation is controlled by gravity, gradients of stress, pressure and temperature, and material rheology, describing how materials deform or “flow”. Understanding the scaling between large-scale deformation and first principle theories and microscopic - sometimes at the atomic scale - mechanisms controlling rheology is key to making predictions about geological processes. For example, understanding what controls the rheology of fault materials provides insights into the nucleation, propagation and arrest of earthquakes.

Unfortunately, geological processes are complex systems where the macroscopic behavior emerges from the behavior of a myriad of microscopic interactions and processes. Thus, many geological processes lack first principle theories and a deep understanding of microscopic mechanisms. For example, several recent earthquakes have challenged our understanding of earthquake mechanics, and new large geophysical datasets show that what we call “earthquake” manifests a complexity that is far beyond our comprehension. However, in the last twenty years, computational power, the availability of big data and new analytical technologies have boomed. In the era of data science, we have models describing complex systems and the possibility of processing massive datasets. We can observe the deformation of rock samples with X-rays in situ, and remote sensing constantly improves, providing better models of large-scale deformation. In the face of such massive resources, we risk concentrating mainly on the data, overlooking the importance of chasing first principle theories and understanding microscopic mechanisms. Bringing together different points of view, from large-scale large-dataset observations to microscopic observations and in between, will further our understanding of geological processes.

We seek for contributions on the wide topic of rheology of geomaterials, including observations at different scales, capable to provide a state-of-the-art tool to interpret macro-scale deformation in light of microscopic mechanisms and first-principles theories. Accordingly, we encourage contributions covering laboratory, modeling, and field observations, with a primary focus on the deformation of the lithosphere on Earth and other planetary bodies. The following, but not limited to, are some of the topics of interest:

• Large strain brittle deformation in rocks and ice, bifurcation theories, rheology and friction of faults;
• Large strain ductile deformation, diffusion creep, dislocation creep, mechanical twinning/kinking, grain boundary sliding;
• Small strain deformation and rheology, attenuation and dispersion of seismic waves;
• Laboratory methods and experiments to study rheology; and
• Field methods and experiences to study rheology.

Topic editor Nicola Tisato is affiliated with the University of Texas at Austin, is a consultant and holds options of SEISMOS Inc. All other Topic Editors declare no competing interests with regards to the Research Topic subject.