HR: 0800h
AN: S31B-0441 [Abstracts]
TI: Rupture process and strong ground motions of the 2007 Niigataken Chuetsu-Oki earthquake -Directivity pulses striking the Kashiwazaki-Kariwa Nuclear Power Plant-
AU: * Irikura, K
EM: irikura@geor.or.jp
AF: Aichi Institute of Technology, 1247 Yachigusa, Yakusa-cho, Toyota, 470-0392, Japan
AU: Kagawa, T
EM: kagawa@geor.or.jp
AF: Geo-Research Institute, 4-3-2 Itachibori, Nishiku, Osaka, 550-0012, Japan
AU: Miyakoshi, K
EM: ken@geor.or.jp
AF: Geo-Research Institute, 4-3-2 Itachibori, Nishiku, Osaka, 550-0012, Japan
AU: Kurahashi, S
EM: q05801@aitech.ac.jp
AF: Aichi Institute of Technology, 1247 Yachigusa, Yakusa-cho, Toyota, 470-0392, Japan
AB:
The Niigataken Chuetsu-Oki earthquake occurred on July 16, 2007, northwest-off Kashiwazaki in Niigata
Prefecture, Japan, causing severe damages of ten people dead, about 1300 injured, about 1000 collapsed
houses and major lifelines suspended. In particular, strong ground motions from the earthquake struck the
Kashiwazaki-Kariwa nuclear power plant (hereafter KKNPP), triggering a fire at an electric transformer and other
problems such as leakage of water containing radioactive materials into air and the sea, although the radioactivity
levels of the releases are as low as those of the radiation which normal citizens would receive from the natural
environment in a year.
The source mechanism of this earthquake is a reverse fault, but whether it is the NE-SW strike and NW dip or the
SW-NE strike and SE dip are still controversial from the aftershock distribution and geological surveys near the
source. Results of the rupture processes inverted by using the GPS and SAR data, tsunami data and teleseismic
data so far did not succeed in determining which fault planes moved.
Strong ground motions were recorded at about 390 stations by the K-NET of NIED including the stations very
close to the source area. There was the KKNPP which is probably one of buildings and facilities closest to the
source area. They have their own strong motion network with 22 three-componentsf accelerographs locating at
ground-surface, underground, buildings and basements of reactors.
The PGA attenuation-distance relationships made setting the fault plane estimated from the GPS data generally
follow the empirical relations in Japan, for example, Fukushima and Tanaka (1990) and Si and Midorikawa
(1999), even if either fault plane, SE dip or NW dip, is assumed. However, the strong ground motions in the site of
the KKNPP had very large accelerations and velocities more than those expected from the empirical relations.
The surface motions there had the PGA of more than 1200 gals and even underground motions at the
basements of the reactors locating five stories below the ground had the PGA of 680 gals.
We simulated ground motions using the characterized source model (Kamae and Irikura, 1998) with three
asperities and the empirical Greenfs function method (Irikura, 1986). Then, we found that the source model
should be a reverse fault with the NE-SW strike and NW dip to explain the strong motion records obtained near
the source area. In particular, strong ground motions in the site of the KKNPP had three significant pulses which
are generated as directivity pulses in forward direction of rupture propagation. This is the reason why the strong
ground motions in the site of the KKNPP had very large accelerations and velocities. The source model is also
verified comparing the observed records at the KKNPP with the numerical simulations by the discrete
wavenumber method (Bouchon, 1981).
DE: 7212 Earthquake ground motions and engineering seismology
SC: Seismology [S]
MN: 2007 Fall Meeting