The Generation Mechanism and Some Properties of the X Phase

Abstract

The generation mechanism of X_3 was investigated. It was concluded that X_3 is a packet of spheroidal overtones. It was already proved in the previous study that X_1 and X_2 are composed of successive arrivals of converted body waves while X_4 is a packet of spheroidal overtones. From the point of view that X_3 and X_4 can be treated as higher modes, the velocity dispersions of X_3 and X_4 were examined. The results show that group velocities of X_3 and X_4 separate into segments corresponding to the extrema of velocity dispersion curves of some higher Rayleigh modes. It can be said that X_3 and X_4 are composed of Airy phases of some higher Rayleigh modes. As to X_l and X_2, the relation between the predominant periods and magnitudes was examined. The results exhibited an correlation between them. The predominant periods of X_1 and X_2 are related directly to the duration of the source process. It was also revealed that the predominant periods grow longer under the influence of focusing of seismic rays.