The statement -- "Historically, 60% of major earthquakes (magnitude 7 or greater) occur during the 14% of the year when the tidal forces are near their maximum" -- on the Wikipedia website about earthquake prediction references the following source:

John H. Glaser (May 2003). "Tidal correlations of seismicity". Geology: Online Forum - Breathing of the seafloor: pp. e3.

Barbara