High-resolution aftershock observations in the source region of the 2004 mid-Niigata Prefecture Earthquake

Aitaro Kato, Masakatsu Arao, Keisuke Ariyoshi, Youichi Asano, Keiji Doi, Bogdan Enescu, Shinya Fujieda, Hiroko Hagiwara, Toshio Haneda, Akira Hasegawa, Shin'ichi Hashimoto, Satoshi Hirahara, Naoshi Hirata, Yasuhiro Hirata, Issei Hirose, Shusaku Hondo, Kumiko Hori, Shuichiro Hori, Shigeki Horiuchi, Toshihiko IgarashiTakashi Iidaka, Yoshihisa Iio, Ryoya Ikuta, Takeo Ito, Takaya Iwasaki, Aya Kamimura, Toshihiko Kanazawa, Yasuyuki Kano, Hiroshi Katao, Satoshi Kawamoto, Tomonori Kawamura, Saeko Kita, Masaru Kobayashi, Yuhki Kohno, Toshio Kono, Masahiro Kosuga, Atsuki Kubo, Eiji Kurashimo, Satoshi Matsumoto, Takeshi Matsushima, Toru Matsuzawa, Noa Mitsui, Reiko Miura, Masatoshi Miyazawa, Tomoko Mizukami, Satoko Murotani, Satoru Nagai, Junichi Nakajima, Takashi Nakayama, Hiroaki Negishi, Kinya Nishigami, Izumi Ogino, Shiro Ohmi, Tomomi Okada, Hiroki Onaha, Shantha S.N. Gamage, Mamoru Saka, Shin'ichi Sakai, Katsuhito Sato, Toshiya Sato, Masato Serizawa, Takuo Shibutani, Junpei Shimizu, Junichi Suganomata, Kiyoko Tagami, Keisuke Takahashi, Kaori Takai, Fumiaki Takeuchi, Yasuda Takumi, Kazuo Tanaka, Ken'ichi Tatsumi, Takashi Tonegawa, Hiroaki Tsushima, Naoki Uchida, Kenji Uehira, Tomotake Ueno, Norihito Umino, Hiroo Wada, Kazutoshi Watanabe, Shigeru Watanabe, Yasuo Yabe, Tadashi Yaginuma, Mamoru Yamada, Shunroku Yamamoto, Yoshiko Yamanaka, Futoshi Yamashita, Fumihito Yamazaki, Satoshi Yui, Yohei Yukutake

Research output: Contribution to journalArticle

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Abstract

We deployed an extremely dense temporal seismic network in the source region of the 2004 mid-Niigata Prefecture Earthquake (thrust fault) on October 23, 2004, Japan. The seismic network consisted of 145 temporary seismic stations within a 30 km squared and had been kept within approximately a month after the mainshock. High accurate hypocenters of 708 events were determined by inverting the arrival times using double-difference earthquake location algorithm. The aftershocks along the mainshock (Mw = 6.6) and the largest aftershock (Mw = 6.3) rupture zones are distributed on two 60° westward-dipping planes, located approximately 5 km apart. Conversely, the Oct. 27 aftershock (Mw = 5.8) occurred on an eastward dipping plane with a dip angle of 25° that was conjugate to the mainshock fault plane. Most of aftershocks at both northeastern and southwestern edges occurred at shallow depths with eastward-dipping planes. Epicenters of aftershocks in the southwestern region are aligned along N15°E, and rotate approximately 20° counterclockwise from the strike of the mainshock fault. This rotation of the aftershock alignments coincides with the rotation of anticline axes in the southwestern area of the source region. Furthermore, distributions of station corrections for a one-dimensional velocity model suggest that the seismic velocity at the western side of the Muikamachi-fault is lower than that at the eastern side. It is also inferred that the velocity structures in the hangingwall vary along the fault strike. The average velocity in the mainshock rupture area is higher than the periphery in the hangingwall, especially compared with the southwestern side of the hypocenter.

Original languageEnglish
Pages (from-to)923-928
Number of pages6
Journalearth, planets and space
Volume59
Issue number8
DOIs
Publication statusPublished - 2007

All Science Journal Classification (ASJC) codes

  • Geology
  • Space and Planetary Science

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    Kato, A., Arao, M., Ariyoshi, K., Asano, Y., Doi, K., Enescu, B., Fujieda, S., Hagiwara, H., Haneda, T., Hasegawa, A., Hashimoto, S., Hirahara, S., Hirata, N., Hirata, Y., Hirose, I., Hondo, S., Hori, K., Hori, S., Horiuchi, S., ... Yukutake, Y. (2007). High-resolution aftershock observations in the source region of the 2004 mid-Niigata Prefecture Earthquake. earth, planets and space, 59(8), 923-928. https://doi.org/10.1186/BF03352030