In March of 2018, a class of 12 Geology and Geophysics seniors from the University of Nevada, Reno conducted geophysical research at Project Shoal, a 1963 nuclear test site. The 12 kT nuclear device produced a cavity at 350 m depth with a 25 m radius, which collapsed within the next few months to within 250 m of the surface.
The class predicted that the collapse chimney would show a 0.17 mGal gravity low and a 2 nT magnetic low, and they measured gravity and magnetic lines across the Shoal ground zero. Back in the classroom the students will determine whether their data have sufficient accuracy to identify those anomalies. They also conducted hammer reflection-refraction surveys at ground zero and 200 m away. They discovered a possible reflection appearing from the top of the collapse chimney at about an eighth of a second two-way travel time. Shallow refraction microtemor arrays may suggest whether there may be incipient collapse closer to the surface.
To conduct this research, PI John Louie, Professor of Geophysics at UNR, borrowed 30 Texans with 4.5 Hz vertical geophones from the IRIS PASSCAL Instrument Center. Using this equipment the class recorded two deep refraction microtremor arrays 2 km long, centered across Shoal ground zero. The Texan data will be released as soon as the class can generate the metadata.
