Shallow seismic refraction survey in the upper Green Lakes Valley catchment at the base of a rock glacier.

Geophysics field plan for each catchment.

Electrical resistivity tomography data describes the distribution of the substrata.

Velocity structures constructed from seismic data showing layering in the critical zone with drill core and hand samples to guide the interpretation.

 

Geophysical surveys allow us to study the structure of the critical zone over large areas without disrupting the soil profile. These surveys provide context for the biological, geochemical and hydrological functions driving weathering and transport within the catchments.

 

 

 

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We employ multiple geophysical techniques to obtain measurements of complementary physical properties, including degree of water saturation and depth of soil, weathered material, and bedrock. Natural outcrops, core samples, and down-hole surveys at drilling sites in each catchment provide a standard (ground truth) to compare our more laterally extensive geophysical results.

 

 

 

 

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Shallow seismic refraction exploits the acoustic properties of materials to image the subsurface. This method is especially useful for delineating the boundary between regolith and bedrock.

Ground penetrating radar uses an electromagnetic pulse to very effectively image detailed layering within the critical zone.

 

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Electrical resistivity tomography measures the resistance of current to flow through the subsurface, which is heavily influenced by water content and rock or sediment type. This apparent resistivity is converted to specific or true resistivity through an inversion process.

 

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Electromagnetic surveys measure similar properties to electrical methods, but depend on magnetically induced currents. These surveys measure lateral variations in ground conductivity in the upper 6 meters of the subsurface.

 

Written by Kevin Befus