Premonitory Variations in S-Wave Velocity Anisotropy before Earthquakes in Nevada

Application of nonhydrostatic stress to rock induces velocity anisotropy, causing the S wave to split into two components traveling with somewhat different velocities. Large premonitory changes in the extent of S-wave splitting have been observed for two earthquakes in Nevada. Observations of the difference between the two S-wave velocities may provide a simple method for pedicting earthquakes.