Abstract
The fundamental principle of the dynamical method consists in the application of vibrations generated by an oscillator set up on the ground surface. The oscillator, designed by the writer, consists of three steel-plate wheels, each 20cm in diameter, to which are bolted lead plated in order to produce an unbalance force. The sinusoidal elastic waves are generated in the ground. The amplitudes and phase differences at various points in the field under investigation are measured with sensitive electro-magnetic seismographs. Investigating the dynamical amplitude-distance and time-distance curves, the writer determined dynamical qualities-i. e., phase velocity, natural frequency and bedding value of the soil. Method of measurments and analysis of the field data are explained in detail with respect to the actual examples carried out near the Tokyo Station in Aug. 1950.
