On The Generation Mechanism of The X Phase

Abstract

From the May 23, 1989 Macquarie Ridge earthquake, repetitions of the X phase were clearly recorded by the long period seismic wave observation system in operation at the Osakayama Crustal Deformation Observatory. The wide dynamic range and the special triggering algorithm of the system allowed recording repetitions from the first order to 6th order. Though the X phase is treated as a packet of spheroidal overtones a priori and utilized to estimate geophysical parameters, however, its generation mechanism has not been investigated in detail. In this paper, it was attempted to clarify the generation mechanism of the X phase. The records obtained were corrected with deconvolution filters in the time domain in order to minimize the influence of instrumental response characteristics. Spectra, particle motion, travel times and apparent velocities were examined. It was concluded that X_1 and X_2 are composed of successive arrivals of converted body waves, and X_4 may be a packet of spheroidal overtones.