We analyze the source mechanism of a deep earthquake beneath Japan on January 1, 1984, whose Harvard centroid moment tensor (CMT) solution significantly deviates from a double couple mechanism. The broadband P-wave ground displacement records show the presence of several distinct phases whose relative amplitudes vary among the stations. We perform very broadband waveform analyses over four different frequency bands: CMT inversion (surface waves (4-5mHz) and long-period body waves (12--20mHz), the waveform inversion using the long-period P, pP and SH waves (~0.04Hz), and broadband P- and pP-wave waveform analysis (0.03~1Hz). We show that the large non double couple solution observed at long periods (>25sec) is very likely to be a manifestation of the presence of subevents with different double couple mechanisms in a single rupture sequence. ¿ American Geophysical Union 1990