Analysis of A Deep “Non Double Couple” Earthquake Using Very Broadband Data

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)), 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 (>25 sec) is very likely to be a manifestation of the presence of subevents with different double couple mechanisms in a single rupture sequence.