抄録
The travel time curve of shallow earthquake gives information about the structure of the earth's crust. But, in usual the observed travel times are plotted against epicentral distances without any consideration on azimuthal differences of observatories with respect to the epicentre. Therefore, by the analysis of the travel time curve made by the above procedure, only vertical irregularities of structure of the earth are obtained in assumption of no lateral irregular structures of the crust. Plots of the observed travel time have some deviations from mean curve in Japan. These deviations seem to contain systematic tendencies which exceed the amount of observation errors. The systematic deviations may be caused by the lateral ununiformness of crustal structure. From this view point, the author attempted a new method of analysis of travel time curves. That is, vertical sections are taken in Japan as in Fig. 1 and the travel time curves of the sections are made from the date of earthquakes and observatories in the belt near the sections. Thus we can easily determined the local characteristics of the structure which derived from analysis of several travel time curves of another section at intersection.
Epicenters of the earthquakes and sections are illustrated in Fig. 1. The crustal structure derived by this method are illustrated in Fig. 2, Fig. 3 and Fig. 4. The present report is a preliminary one satisfying the observed travel times of shallow earthquakes. The more accurate data from the observations of artificial explosions and local earthquakes will give some modification to this structures.
