Abstract

Studying the critical zone is advantageous in understanding how processes in this near-surface layer influences life-sustaining habitats and resources.  The rates of weathering and sediment transport could play an influential role in affecting soil properties and ultimately food and water quality.  To assess whether or not electrical resistivity and seismic P-wave velocities can be modeled and compared to outcrop observations, a 96 m electrical resistivity and 100 m seismic refraction survey were conducted centered over two outcrops.  Outcrop 1 is 2.5 m in height and composed of highly fractured Rose Hill shale.  Outcrop 2 is 2 m in height and composed of less fractured Rose Hill shale.  Both outcrops are covered by a 10 cm thick organic soil section.  Results indicate correlations between field observations and the resistivity model, where Outcrop 1 exhibits a low resistivity (~125 Ohm m) and Outcrop 2 exhibits a higher resistivity (~800 Ohm m).  Inversion of the seismic refraction data used an initial model constrained by P-wave velocities obtained from borehole CZMW10.  The P-wave model obtained from the inversion shows the top layer (250-400 m/s) correlates with soil and the velocity gradient (750-2000 m/s) correlates with the rock outcrops.  The inversion did not show a difference in P-wave velocities between the two outcrops.  This study concluded that the resistivity model was able to “ground-truth” the field observations more precisely than the seismic refraction model.

Citation

Schuler, Nicholas (2019): Ground-truthing Subsurface Variations in Seismic Velocities and Electrical Resistivity using Outcrop Observations, Susquehanna Shale Hills Critical Zone Observatory. Bachelor of Science, Geosciences, The Pennsylvania State University.