1231 earthquakes have taken place in and near Japan from 1885 through 1963 which were 6.0 or more in magnitude. The points which are plotted in Fig. 4 according to year represent the cumulative sum of energy which has been released by earthquakes since the beginning of 1885 until the end of the year to which each of the points refers. The points are bounded between two parallel straight lines, of which the upper one is expressed by
y=(2.24t+1.91)×10²³erg,
where t is the number of years counted from 1885. The distance between the upper and lower lines corresponds to about 25×1023erg which is very close to the energy of the largest conceivable earthquake. Fig. 5 shows the year-to-year variation of the deviation Δ of each point from the line S in Fig. 4. This deviation is interpreted as representing the amount of energy which is stored in the crust or the mantle of the earth from which earthquakes originate. In Fig. 5, the amount of energy actually released by earthquakes in each year is compared with the deviation Δ for the previous year. Large earthquakes are seen to have occurred when the deviation for the previous year had been large. No large earthquakes have occurred when the deviation for the previous year had been small.