Findings and lessons learned while translating statistical physics to Soft Earth materials*

A hallmark of many processes within Earth's subsurface is the transitions in states that natural granular materials undergo, from structurally arrested to creeping to flowing. These transitions in material states can produce geohazards (e.g., landslides, ground-rupturing earthquakes, and liquefaction) that cause loss of life and destroy infrastructure. Using continuum models primarily, the geoscience community has yet to identify reliable ways to forecast if, when, and how structurally arrested buried sediments will creep, flow, and or suddenly fail. Granular physics research indicates that the relationships between shear stress and the spatial distribution and magnitude of mesoscale features such as interparticle friction, pore pressure, force chain distribution, and coordination number exert control on the rigidity and flow of lab-reconstituted and simulated granular materials (e.g., a column of 2-D disks or glass spheres). Thus, a natural next step for the geoscience community is to assess whether such tools, developed for more idealized systems, are useful for studying natural granular materials, which tend to be more disordered. This talk discusses findings and lessons from viewing natural earth materials through a granular lens. Specifically, we report on the use of a series of field and lab experiments to assess the degree to which (1) energy serviced during deposition influences the configurational geometry, strains, and rigidity of natural earth materials, (2) whether the frictional jamming framework for forecasting transitions between solid-like and fluid-like states provides insights into the development and erasure of deformation memory and granular flow within shallow fault zones, (3) whether various forms of entropies provide useful ways to characterize the geometric complexities of natural granular materials, and (4) whether the density of excited vibrational modes, which has been shown to provide a potential precursor signal to unjamming, may be extracted from seismograms collected within natural sediments. The main lessons are that there are significant benefits to viewing the Earth through a granular lens and to working interdisciplinarily to improve existing granular physics frameworks so they capture the hysteresis and disorder within natural granular materials.