@misc{indiciaea9382585dac6,
  title = {Seismic detection of near-surface cavities},
  author = {J. S. Watkins and R. H. Godson and Kenneth Watson},
  year = {1967},
  doi = {10.3133/pp599a},
  url = {https://pubs.usgs.gov/publication/pp599A},
  note = {Source identifier: pp599A}
}