INITIAL PHASE-ANALYSIS OF R-WAVES FROM GREAT EARTHQUAKES

Phase equalization was carried out for R waves in order to obtain information on source mechanisms of four earthquakes, the Kurile earthquake of 1963, its largest aftershock, the Rat Island earthquake of 1965, and the Tokachi-oki earthquake of 1968. The initial phase was computed using the corresponding complete great-circle phase velocity, so that influences of the lateral heterogeneity of the earth's structure were considerably reduced. The fault length o the Kurile earthquake was determined from the initial phase radiation pattern on the basis of a simple propagating fault model. There is no trade-off in this method between the fault length and the rupture velocity. Such a trade-off is inherent to the conventional directivity method. A fault length of 250 km was obtained, which was found to be nearly equal to the length of the aftershock area. We have introduced a dynamic fault parameter 'source time' that can be determined from the phase measurement using the complete great-circle phase velocity rathe than the average phase velocity of the individual multiple R waves. This quantity corresponds to the rise time of the source time function of an equivalent point source. Source times of 97, 62, 174, and 115 s were obtained for the above four earthquakes. -Author