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Seismological Notes

Nature volume 68, page 235 (09 July 1903) | Download Citation



IN the nineteenth report of the Tokio Physico-mathematical Society Dr. F. Ōmori, gives two short papers on the velocity with which earthquake waves are propagated. In calculating these velocities it is assumed that the paths followed are in all cases arcual, and that a correct velocity is arrived at by dividing the distance between Tokio and a station in Europe by the difference in time at which similar phases of movement were recorded at two such places. As to the soundness of this method, excepting as applied to the large waves of earthquakes, opinions vary. In another note by the same investigator, attention is drawn to the difference in the character of seismograms obtained at two stations about a mile apart. At one station, two distinct groups of maximum movements are shown. These are explained as the longitudinal and transverse components of elastic vibrations simultaneously produced at the seismic centre. At the other station the records are described as a series of maximum movements at fairly regular intervals. This feature is attributed to a rhythmic interference between the proper oscillation of a soft surface soil and the movements of an underlying harder ground. In a discussion on pulsations or small movements of non-seismic origin, it is shown that the period of these corresponds to the period of preliminary tremors, from which it is inferred that for both of these movements their periods depend upon the nature of the soil where they are observed.

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