Earth Planets Space, Vol. 60 (No. 11), pp. 1087-1091, 2008LETTER
Takeshi Iinuma1, Yusaku Ohta1, Satoshi Miura1, Kenji Tachibana1, Takeshi Matsushima2, Hiroaki Takahashi3, Takeshi Sagiya4, Takeo Ito4, Shin'ichi Miyazaki5, Ryosuke Doke6, Akira Takeuchi6, Kayo Miyao1, Akihiko Hirao2, Takahiro Maeda3, Teruhiro Yamaguchi3, Masamitsu Takada3, Makiko Iwakuni5, Tadafumi Ochi5, Irwan Meilano4, and Akira Hasegawa1
1Research Center for Prediction of Earthquakes and Volcanic Eruptions, Tohoku University, Sendai 980-8578, Japan
2Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, Shimabara 855-0843, Japan
3Institute of Seismology and Volcanology, Hokkaido University, Sapporo 060-0810, Japan
4Research Center for Seismology, Volcanology and Disaster Mitigation, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8602, Japan
5Earthquake Research Institute, the University of Tokyo, Tokyo 113-0032, Japan
6Department of Earth Sciences, Faculty of Science, University of Toyama, Toyama 930-8350, Japan
(Received November 30, 2007; Revised February 4, 2008; Accepted February 26, 2008; Online published November 18, 2008)
Postseismic crustal deformation associated with the 2007 Chuetsu-oki Earthquake, which occurred on 16 July 2007 with a magnitude of 6.8 at the southeastern rim of the Sea of Japan, near the coast of Mid-Niigata Prefecture, Central Japan, are detected by GPS observations. We analyzed continuous GPS data from the sites of the Geographical Survey Institute of Japan (GSI) and another dense temporary network, which we established just after the main shock to reveal spatio-temporal evolution of postseismic slip for 50 days after the main shock by geodetic inversion methods. Four models of faults are configured following Ohta et al. (2008, this issue), and these are optimized based on ABIC (Akaike's Bayesian Information Criterion). The results of the inversion analysis show that the postseismic slip on the faults occurred at a downdip and updip extension of the coseismically slipped portion. The slip in the shallower portion decayed to be negligible within 2 weeks, and the slip in the deeper portion was still large after the slip in the shallower portion had almost terminated.
Key words: Crustal deformation, postseismic slip, GPS, strain concentrated zone, Niigata-Kobe Tectonic Zone.