Earth Planets Space, Vol. 58 (No. 1), pp. 37-43, 2006
Haruko Sekiguchi1, Shin Aoi2, Ryou Honda3, Nobuyuki Morikawa2, Takashi Kunugi2, and Hiroyuki Fujiwara2
1Active Fault Research Center, GSJ, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8567 Japan
2National Research Institute for Earth Science and Disaster Prevention 3-1 Tennodai, Tsukuba, Ibaraki, 305-0006 Japan
3 Hot Springs Research Institute of Kanagawa Prefecture 586 Iriuda, Odawara, Kanagawa, 250-0031, Japan
(Received September 5, 2005; Revised December 8, 2005; Accepted December 12, 2005; Online published January 27, 2006)
We have investigated the rupture process of the 2005 West Off Fukuoka Prefecture earthquake by the multi-time- window linear waveform inversion method using the strong ground motion data recorded at 11 K-NET and KiK-net stations. From the waveforms of the P-wave portion, it is indicated that the energy release in the first few seconds was markedly lower than the subsequent part, and this causes difficulty in identifying onset of the S-wave. To decide an appropriate time window for the waveform inversion, we estimate the S-wave onset using aftershock records. The inverted slip distribution shows a single asperity of 8 km × 6 km and its center located 8 km to the southeast and 6 km above the hypocenter. The asperity explains most of the large-amplitude signals in the observed waveforms. The turning point from the initial low-energy-release rupture to the main high-energy-release rupture is estimated from the spatial variation of the observed initial rupture phase. It is found 3.3 s after the initiation of the rupture at about 4 km to the southeast of the hypocenter. Stress drop during the initial rupture is estimated to be in the same order of those of moderate size aftershocks, which indicates that the initial rupture is an ordinary dynamic rupture.
Key words: The 2005 West Off Fukuoka Prefecture earthquake, rupture process, strong motion, K-NET, KiK-net.