@misc{indiciae8b4ce6545a3c,
  title = {A formulation of directivity for earthquake sources using isochrone theory},
  author = {Paul Spudich and Brian S.J. Chiou and Robert Graves and Nancy Collins and Paul Somerville},
  year = {2004},
  doi = {10.3133/ofr20041268},
  url = {https://pubs.usgs.gov/publication/ofr20041268},
  note = {Source identifier: ofr20041268}
}