An analysis is made of the body waves radiated by the Niigata earthquake of June 16, 1964, (M=7.5) for the study of its source mechanism. By means of the least squares method, the fault plane solutions are obtained from the S wave data for both of the main shock and one of its aftershocks, July 12, 1964, (M=6.0). It is found that the earthquake mechanism of the main shock can be explained by a model of almost pure dip-slip on the basis of the double couple hypothesis, and that the mechanism of the aftershock is similar to that of the main shock.
A particular type of phase is found in the P wave-train around 20 seconds after the first arrival, which shows the distinctive characteristics of the stopping phase. By interpreting the arrival time differences between the stopping phases and the first arrivals as a function of the azimuth of the observation point, it is concluded that the earthquake fracture was propagated with a velocity of 2.0±0.4km/sec through a distance of 40±10km in the horizontal direction of N 10°.5E. Although quantitative results cannot be obtained for the faulting in the opposite direction, it is evident that a bilateral model is appropriate for explaining the earthquake.
The partition of P wave energy per unit solid angle in certain ranges of frequency observed at some selected stations are explained by adopting a symmetrical bilateral model. The total wave energy radiated by the earthquake is estimated to be 3.2×1022 to 2.0×1022erg. Assuming that the vertical extension of the fault is 20km, the magnitude of the displacement discontinuity along the fault is calculated at 4.5 to 5m.
Based on the concept of continuous distribution of infinitesimal dislocations, the static potential energy due to the residual strain field after the earthquake is estimated to be 7.2×10²² to 6.8×10²²erg. The average strain within the width of the dislocations is evaluated at 6×10-4 to 3×10-4.

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In the field of seismic prospecting there is an urgent need to minimize the man power of experienced people for drawing a travel time curve of explosion observation. Otherwise the speed of the data accumulation exceeds that of the data processing, and data sit on desks permanently. Here a simple computer oriented method is suggested, which is similar to the method of least squares, but the result is not affected by points far from the straight line which is the true travel time curve.

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