@misc{indiciae946dbbae07c7,
  title = {The international seismological observing period in Africa},
  author = {E.R. Engdahl and Eric A. Bergman},
  year = {1992},
  doi = {10.1016/0040-1951(92)90003-o},
  url = {https://pubs.usgs.gov/publication/70017152},
  note = {Source identifier: 70017152}
}