Figure 8 Three compaction, without crushing mechanisms: 1) grain rotation, 2) ductile compression of grains, or 3) compression of pressured pore space (the transition of an over-pressured state to a grain supported frame).
The problem then is how, through these limited mechanisms, can the rock realize the necessary broad distribution of characteristic relaxation times? It seems reasonable that both mechanisms may enjoy some breadth in time-scale simply as function of heterogeneity of mineralogy and sorting. To truly achieve the smooth single mode distribution required however implies that the ductile grains act as impulse sensitive springs and the grain rotation is almost fractal. These requirements seem difficult enough to achieve without the further requirement that they overlay and interact nicely together.
The experiments shown here are all done on manufactured plugs of frozen loose river sand described as sub-angular, moderately well sorted, feldspathic and fine grained. Similar tests on Gulf turbidite reservoir core samples show similar results.
It is my suggestion then to perform a similar suite of tests on manufactured grain packs in an effort to understand how the various mechanisms are responsible for which parts of the scaling phenomenon. To this end samples of various sorting, grain size, grain shape, mineralogy, and combinations of all of the above could be manufactured and tested under uniaxial strain tests. A further help in identifying the processes involved would be to take intermediate images of the sample to show the nature and state of the undergone transformations similar to Cadoret's partial saturation experiments (from Mavko (2001)).
Further, once these processes and their limiting and defining characteristics are well understood, the development of type curves for various material would be very valuable.