Regolith, rock and fluid distributions at the Upper Colorado River Basin via a multicomponent seismic imaging approach

The depth to, and physical properties of, soil, weathered bedrock, and competent bedrock in the Upper Colorado and many other mountainous watersheds, can play a significant role in subsurface water fluxes and storage. While quantification of bedrock characteristics is recognized as a critical component for predicting watershed function, characterization of key subsurface properties at sufficient resolution, yet over large spatial extents, is currently not standard practice. We suggest that geologic conditions at the local scale strongly control slope, soil distributions, soil and rock porosity, hydraulic conductivity, and fluid distributions in this shale dominated geologic system. With this proposal, we will explore the interplay between rock properties, weathering, and fluid flow paths for a shallow mountainous aquifer system via rapid multicomponent seismic measurements.

Geotechnical and hydrogeophysical studies have shown regional and local correlations between shear wave velocity and slope, elevation and geological conditions (e.g., Thompson et al., 2014). Observations regarding slope, weathering and fluid distributions have been made using p-wave velocities (e.g., Hyndman et al., 2000; Befus et al., 2011; St Clair et al., 2015). Discrete and independent Vp or Vs measurements are the current standard for geomorphologic and geologic comparisons, yet relationships between porosity, confining pressure and fluids are best highlighted and better constrained by Vp, Vs and their ratios at regional scales (e.g., Lee, 2003; Catchings et al., 2014). Further improvements are possible by integrating seismic reflection profiling, surface electrical, and borehole seismic measurements. Joint collection of Vp, Vs and reflection data in 2-D at a rapid pace with the use of a Boise State University developed seismic land streamer system will best determine relationships between surface and subsurface properties at both local and regional scales. These measurements, in turn, will help constrain flux and storage properties in the Upper Colorado watershed that can then be applied to, and compared with, other mountainous watersheds.