Electrical resistivity tomography (ERT) and horizontal-to-vertical spectral ratio (HVSR) data collected East and Southeast of Ellsworth Air Force Base, South Dakota, in 2021

This data release contains electrical resistivity tomography (ERT) and passive seismic data collected east of Ellsworth Air Force Base, South Dakota, from April to September 2021. The data accompanies a USGS scientific investigations map from Medler (2022). The U.S. Geological Survey, in cooperation with the U.S. Air Force Civil Engineer Center, used surface geophysical methods to delineate the top of the Cretaceous Pierre Shale along survey transects in selected areas east of Ellsworth Air Force Base, South Dakota. In 2021, the U.S. Geological Survey performed passive seismic and 2D electrical resistivity tomography (ERT) surveys along 21 co-located survey transects east of Ellsworth Air Force Base. Passive seismic data were analyzed using the horizontal-to-vertical spectral ratio (HVSR) method in the Grilla software suite (https://moho.world/en/) to determine the fundamental resonance frequency peak at each site. Passive seismic data were also collected at existing well sites and the average shear wave velocity for unconsolidated deposits overlying the Pierre Shale was used to calculate the depth to Pierre Shale along survey transects. ERT data were processed using EarthImager2D software from Advanced Geosciences, Inc. (https://www.agiusa.com/agi-earthimager-2d) to remove noisy measurements and produce subsurface resistivity profiles that were interpreted to estimate the depth to the Cretaceous Pierre Shale. HVSR results were plotted with ERT profile results to delineate a continuous bedrock surface for each survey transect. The continuous bedrock surface results were converted to elevations using light detection and ranging (liDAR) elevation data and were extracted to electrodes locations that were part of ERT surveys for each survey transect. The unprocessed and processed data for each geophysical surveys and bedrock delineation are provided as either comma-separated values (.csv) files or zipped folders (.zip) and annotated accordingly in the metadata.