Evidence for non-self-similarity and transitional increment of scaled energy in the 2005 west off Fukuoka seismic sequence

摘要

We investigated seismic scaling relations of the 2005 west off Fukuoka seismic sequence in Japan using a coda-based methodology. Two independent methods such as coda sourcc spectrum method and coda spectral ratio method were applied to seismic waveform data recorded at four broadband seismic stations located around the epicenter of the mainshock. The corner frequencies determined from both methods are consistent with each other, and the scaling relations between the corner frequencies and the corresponding seismic moments are clearly nonself-similar in both cases. Moreover, the scaled energy obtained from the coda source spectrum method shows that there is a transitional change in the scaled energy with seismic moment. The scaled energy is larger for events with Mw >5.0 than for events with Mw <4.0. For events larger than Mw 5.0, the scaled energy is almost constant and it means that they obey self-similar scaling. For events smaller than about Mw 4.0, the scaled energy is more or less constant, but it is difficult to decide whether it follows self-similar or non-self-similar scaling because of scatter and the limitation of the minimum moment magnitude (Mw 3.4). The most important observation is a linear increment of the scaled energy between about Mw 4.0 and 5.0. These observations imply that the rupture dynamics for larger and smaller earthquakes arc different and that the change in dynamics may occur continuously between about Mw 4.0 and 5.0 in this seismic sequence.