Defining the base of the Critical Zone: Stress, Topography, Fracture Permeability

Wednesday, 17 December 2014
James Taylor St. Clair1, Seulgi Moon2, W Steven Holbrook3, J Taylor Perron2, Stephen J Martel4 and Kamini Singha5, (1)University of Wyoming, Laramie, WY, United States, (2)Massachusetts Institute of Technology, Cambridge, MA, United States, (3)Univ Wyoming, Laramie, WY, United States, (4)Univ Hawaii, Honolulu, HI, United States, (5)Colorado School of Mines, Golden, CO, United States
Fractures play an important role in groundwater flow and chemical weathering in the deep critical zone. Fracture permeability is sensitive to the state of stress. Large differential stresses may cause fractures to dilate and become more permeable due to opening mode displacement or shear displacement along irregular surfaces. Topographic perturbations of the regional tectonic stress fields have been shown to be large enough to influence the distribution of fractures in the subsurface. Previous studies of topographically influenced stress distributions have suffered from a lack of spatially continuous characterization of the subsurface fracture distribution. Here we compare stress models that account for both topography and the regional stress fields to seismic velocity profiles. We find a strong correlation between failure potential, a normalized measure of differential stress, and the near surface seismic velocity structure. This correlation suggests that critical zone architecture is, to a first order, controlled by topographic perturbations of the regional stress field.