I just pulled out his thesis to check this again, and his results have gained no validation in the years since it was published, which was 1999 (nor before then).

Chapter IV hypothesizes that source regions of large earthquakes are reactivated as seismic phases return. He's guessing that aftershock rates take a small jump as inconsequential phases return. Table 15, for example, lists events allegedly triggered by P reflections from the inner and outer core. Figure 27 includes the claim that the P wave reflected 4 times off the 670-km-depth discontinuity triggers significant activity. It takes an array to spot a wave that reflects once, and the wave loses 90% of its amplitude and 99% of its energy with each bounce.

Chapter V, the only other plausibly connected with seismic waves triggering distant earthquakes, considers only 10 degrees and farther distances. He claims enhanced triggering at 10, 18, 35, 40, 60, 70, 100, 120, 160, and 180 degrees distance.

We now know that observed triggering in Landers and Denali is done by the surface waves, as one would expect, given that they carry the vast majority of the stress in the earthquake waves, not the body waves Whiteside hypothesized. There is no good reason for surface wave amplitudes to systematically peak up at particular distances aside from 180 degrees, and I've seen no evidence for such antipodal triggering.

The surface-wave triggering rates are far too small to be useful for prediction.