Earth Planets Space, Vol. 60 (No. 10), pp. 1011-1016, 2008LETTER
Takahiro Maeda1, Masayoshi Ichiyanagi1, Hiroaki Takahashi1, Ryo Honda1, Teruhiro Yamaguchi1, Minoru Kasahara1, and Tsutomu Sasatani2
1Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University, N10W8 Kita-ku, Sapporo 060-0810, Japan
2Graduate School of Engineering, Hokkaido University, N13W8 Kita-ku, Sapporo 060-8628, Japan
(Received June 30, 2007; Revised December 6, 2007; Accepted January 8, 2008; Online published November 7, 2008)
A large crustal earthquake, the 2007 Noto Hanto earthquake, occurred west off the Noto peninsula in Ishikawa prefecture, Japan, on March 25, 2007. We started temporary strong motion observation at five sites within the aftershock area from about 13 h after the main shock occurrence. We first applied the spectral inversion method to S-wave strong ground motion records at the temporary and permanent stations. We obtained source specta of the main shock and aftershocks, Qs (quality factor for S-wave) values (Qs = 34.5f0.95) and site responses at 22 sites. We then estimated a source model of the main shock using the empirical Green's function method. The source model consists of three strong motion generation areas and well explains the observed records. Finally, we examined the consistency of the main-shock source models estimated from the above two analyses. The high-frequency level of the acceleration source spectrum based on the main-shock source model is consistent with the source spectrum estimated from the spectral inversion. The combined area of strong motion generation areas is approximately half of the value expected by the empirical relationship, and the high-frequency level of acceleration source spectrum is approximately 2.5 times larger than the empirical relationship for shallow inland and inter-plate earthquakes.
Key words: 2007 Noto Hanto earthquake, temporary strong motion observation, spectral inversion method, empirical Green's function method.