Note 57 — Chapter VII · ToC

Professor Omori finds that the mean daily number of earthquakes y during the month x (reckoned from November 1891) may be approximately represented by the equation—

y = 16.9 / (x + 0.397);

or, taking the semi-daily earthquake numbers during the five days between October 29th and November 2nd, 1891, by the equation—

y = 440.7 / (x + 2.314),

where y denotes the number of earthquakes observed during the twelve hours denoted by x, the time being measured from the first half of October 29th. It is interesting to notice that, taking account of the mean annual frequency of earthquakes in ordinary years, the number of shocks observed at Gifu during the two years 1898-99 should, according to the latter formula, be 163; the actual number recorded was 160.