Electrical resistivity tomography (ERT) and horizontal-to-vertical spectral ratio (HVSR) data collected east of Box Elder, South Dakota, in 2021
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 2019, the U.S. Geological Survey performed passive …