Geological faults ihave granular textures on many scales, from microscopic grains to macroscopic rocks. We seek to understand the extent to which granular interactions (interparticle, frictional slip) account for the range of geological observations & the inferred dynamic fault histories.
We conduct laboratory experiments using birefringent (photoelastic) particles in a simulated strike-slip fault. This movie of a laboratory fault experiment shows events in which the abrupt localization of the shear strain to the center of apparatus corresponds to little change in the force chain geometry away from the "fault." Bright particles are experiencing greater force than dark particles.
[This movie] shows an annular fault, and is representative of the pronounced stick-slip behavior we observe in the lab.
Ted Brzinski, postdoc
Most Near-Earth Objects (NEOs) are composed of fracture rock, sometimes so fractured as to be nearer to a granular material than a solid body. These "rubble pile" asteroids are only weakly held together by gravitational forces: a child would be able to throw a ball above the escape velocity!
Spatial patterns of 'dead' lawn grass have often been ascribed to Turing-type reaction-diffusion processes related to water scarcity. We have suggested an alternative hypothesis: that the air within the grass canopy is unstable to a convective instability, such that chill damage caused by falling cold air is responsible for the creation of brown and green bands of grass. This hypothesis is consistent with several features of small-scale vegetation patterns, including their length scale, rapid onset and transient nature. We find that the predictions of a porous medium convection model based are consistent with measurements made for a particular instance of lawn-patterning in North Carolina. In the image at left (courtesy Art Brunneau of the NCSU Turf Science program), it is clear that only the longer grass (taller fluid layer) is subject to this pattern-forming instability, as would be predicted by the convection model we propose.