@misc{indiciae855b820f1978,
  title = {A vacuum hammer seismic source for underground use},
  author = {R. D. Carroll},
  year = {1993},
  doi = {10.1016/0148-9062(93)92223-d},
  url = {https://pubs.usgs.gov/publication/70017503},
  note = {Source identifier: 70017503}
}