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An automatic relay computer for calculating autocorrelation coefficients, based on the simplified method of its computation proposed by Y. TOMODA, has been built for the purpose of analysing seismograms. Seismograms of about one hundred near earthquakes recorded at the Central Meteorological Observatory in Tokyo and at the Mizusawa Latitude Observatory were used for the analyses. Each seismogram was divided into several portions, and within each portion, the dependence of the prodominant period of seismic waves upon the magnitude of the earthquakes and upon the crustal structure of the wave path were studied.
Keiiti Aki (Sun,) studied this question.