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Three-dimensional seismic velocity structure as determined by double-difference tomography in and around the focal area of the 2005 West off Fukuoka Prefecture earthquake

2006; Springer Nature; Volume: 58; Issue: 12 Linguagem: Inglês

10.1186/bf03352672

1880-5981

Maiya Hori, Satoshi Matsumoto, Kenji Uehira, Tomomi Okada, Tomoaki Yamada, Yoshihisa Iio, Masanao Shinohara, Hiroki Miyamachi, Hiroaki Takahashi, Kazuo Nakahigashi, Atsushi Watanabe, Takeshi Matsushima, Norimichi Matsuwo, T. Kanazawa, Hiroshi Shimizu,

Seismic Waves and Analysis

Abstract On March 20, 2005 the West off Fukuoka Prefecture earthquake (magnitude of 7.0 on the JMA scale) occurred in southeastern Japan. The earthquake fault was a left-lateral strike-slip having a nearly vertical fault plane and a strike in the WNW-ESE direction. The largest aftershock with a magnitude of 5.8 (JMA) followed 1 month later. To gain more detailed aftershock data, several teams from different Japanese universities jointly installed a number of temporary seismic stations and positioned Ocean Bottom Seismometers (OBSs) immediately above the focal area. Double-difference tomography was used to estimate the three-dimensional (3D) (Zhang and Thurber, 2003) velocity structures in and around the focal area based on the travel time data collected during seismic observations. The high-velocity regions estimated by the inversion are located on the edge of the aftershock area and on the shallow part of asperity, as inferred from the slip distribution. Conversely, the V p / V s ratio is not always as high as that found at the location of the asperity. This finding suggests that the construction of the medium is not uniformly elastic but complex, with different relations between elastic constants and strength.