Analysis of a deep ``non-double couple'' earthquake using very broadband data,

Kuge, K., and H. Kawakatsu
Geophys. Res. Lett., 17, 227-230, 1990.

Abstract

We analyze the source mechanism of a deep earthquake beneath Japan on January 1, 1984 (9:03 40.1sec, 136.80^oE, 33.62^oN, depth=386.0km, m_b=6.4, ISC), 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)), first motion using the long-period P and SH waveforms (~0.04Hz), and broadband P-wave waveform analysis (0.03~1Hz). We postulate and show that the large non double couple solution observed at long periods (>25sec) is a manifestation of the presence of several subevents with different double couple mechanisms in a single rupture sequence.