Earth Planets Space, Vol. 60 (No. 11), pp. 1093-1098, 2008LETTER
Takuya Nishimura, Mikio Tobita, Hiroshi Yarai, Shinzaburo Ozawa, Makoto Murakami, Toru Yutsudo, Masayoshi Ishimoto, Takeshi Umesawa, Takashi Toyofuku, Satoshi Kawamoto, Tomomi Amagai, Midori Fujiwara, Akira Suzuki, Syunji Enya, Toshiyuki Sasaki, Masanori Yokokawa, Syuichi Oomori, Setsuo Tanoue, Hisao Ikeda, Moriyuki Nemoto, Hisashi Suito, Fumi Hayashi, Hiroshi Une, Mamoru Koarai, and Masaharu Tsuzawa
Geographical Survey Institute, Tsukuba, Ibaraki, Japan
(Received November 30, 2007; Revised June 6, 2008; Accepted June 7, 2008; Online published November 18, 2008)
The 2007 Chuetsu-oki earthquake occurred just west off the coast of Kashiwazaki in Niigata Prefecture, Central Japan on July 16, 2007. The permanent GPS network (GEONET) clarifies the coseismic displacement as a thrust faulting whose compressional axis lies in the NW-SE direction. Interferometric analysis of synthetic aperture radar (SAR) images acquired by "Daichi" satellite (ALOS) maps a detailed spatial pattern of the displacement toward the satellite for both ascending and descending orbits. Peak-to-peak displacement reaches approximately 400 mm in the descending orbit interferometric (In)SAR data. Repeated precise leveling shows uplift near the northeast part of the aftershock area and subsidence near the southwestern part. We construct a preliminary fault model by inverting the observed deformation. The preferred model consists of two segments of rectangular faults whose moment magnitude is 6.7 in total. From only the used geodetic data on land, it is difficult to determine which plane in two conjugate planes of the focal solution was ruptured. It is important to consider the effect of a heterogeneous medium and variable slip on the faults as well as other geophysical data to determine the fault model with confidence.
Key words: 2007 Chuetsu-oki earthquake, crustal deformation, GPS, InSAR, leveling.