Note 59 — Chapter VII · ToC

The periodicity of after-shocks is discussed in the papers numbered 4, 12, 16, and 17 at the end of this chapter. In these, the existence of diurnal and other periods is clearly established. Professor Omori also shows that the mean daily barometric pressure is subject to fluctuations with maxima occurring on an average every 5½ days, and that earthquakes are least frequent on the days of the barometric maxima and minima, and more frequent in the days immediately preceding and following them.