Earth Planets Space, Vol. 60 (No. 11), pp. 1105-1109, 2008LETTER
Yohei Yukutake, Tetsuya Takeda, and Kazushige Obara
National Research Institute for Earth Science and Disaster Prevention, Tennodai, 3-1, Tsukuba, Ibaraki 305-0006, Japan
(Received November 30, 2007; Revised March 18, 2008; Accepted March 24, 2008; Online published November 18, 2008)
The 2007 Chuetsu-oki Earthquake (Mj = 6.8) occurred in the eastern margin of the Japan Sea where high strain rates have been observed and many large earthquakes have occurred. The main shock was located near the Western Nagaoka Basin active fault system dipping in the westward direction. We estimated the well-resolved hypocenter location around the main shock rupture zone from the differential arrival times obtained by both manual picking and waveform cross-correlation analysis. From the relocated aftershock distributions, we successfully resolved the detailed fault structures activated by the main shock. The estimated fault model resolves four individual fault segments. The fault model suggests that the main shock predominantly ruptured the southeastward dipping fault planes. On the other hand, the aftershocks around the hypocenter of the main shock occurred on both the northwestward and southeastward dipping fault planes. Both fault planes around the hypocenter of the main shock may have been nearly coincidentally ruptured during the main shock.
Key words: The 2007 Chuetsu-oki earthquake, aftershocks, hypoDD, fault structure.