In recent years both physicists and geophysicists have become increasingly interested in macroscopic patterns and features that spontaneously form in space and time during the deformation of brittle and granular media. Such features include faults and shear bands in the shearing of brittle and ductile solids and in the deformation of granular media, spontaneous grain size segregation during flow, and a variety of other patterns formed during oscillatory motion. Often these features exhibit self-similarity, and their populations have fractal-size distributions.
These spontaneous formation—or self-organizing—phenomena are hallmarks of what has become known as the physics of complexity. The study of complexity is in its exploratory phase, past its infancy, but nowhere near the point where a general understanding of these phenomena has been achieved. The youth of this topic makes it one of the hottest topics in both geophysics and condensed-matter physics.