Focal Mechanism Analyses of Aftershocks of the 1984 Western Nagano Prefecture Earthquake

Fumihito Yamazaki, Tooru Ooida, Mamoru Yamada, Harumi Aoki, Iwao Fujii, Akira Ikami, Rikio Miyajima, Masaru Nakamura, Fumihito Yamazaki, Tooru Ooida, Fumihito Yamazaki, Akira Ikami, Toru Nakayama, Akira Hasegawa, Toshio Kono, Akio Takagi, Toru Matsuzawa, Shigeki Horiuchi, Shigeki Horiuchi, Tatsuo SaekiYasuhiro Umeda, Yuji Kurata, Akio Kuroiso, Yoshihisa Lio, Kiyosm Ito, Kiyosm Ito, Sadaomi Suzuki, Takeo Moriya, Akihiko Yamamoto, Hiroki Miyamachi, Takeo Moriya, Kinya Nishigami, Kazuro Hirahara, Satoru Kuriyama, Fumiaki Takeuchi, Takuo Shibutani, Hiroo Wada, Takeshi Mikumo, Satoshi Kaneshima, Norio Hirano, Makoto Koizumi, Kazuo Oike, Takahiro Okuda, Kinya Nishigami, Toru Ouchi, Toru Ouchi, Toshikazu Tanada, Manabu Yokohama, Toshikazu Tanada, Ken Ichiro Yamashina, Tameshige Tsukuda, Shin Ichi Hashimoto, Ikuo Karakama, Masaru Kobayashi, Toshio Haneda, Yukio Ishiketa, Katsumi Miura, Kaname Sakai, Megumi Mizoue, Isao Nakamura, Masayoshi Takahashi, Tameshige Tsukuda, Shoji Tomita, Naoshi Hirata, Toshihiko Kanazawa, Tetsuichiro Yabuki, Akihiko Ito, Masayuki Suzuki, Masahiro Kosuga, Kazuaki Miura, Atsushi Nakajima, Toshio Mitsunami, Takuo Okamoto

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Abstract

Focal mechanisms around Ontake Volcano, central Japan, were investigated by using the data set obtained by a seismic observation project of the 1986 Joint Seismological Research in Western Nagano Prefecture (JSR'OG). The data set included P-wave first motions of aftershocks of the 1984 Western Nagano Prefecture Earthquake (M = 6.8) mainh. A total of 556 events was selected for the focal mechanism analysis. The P-wave data from the surrounding university routine networks were also utilized additionally. Four hundred two events were successfully analyzed. Based on the types of focal mechanisms and on the spatial distribution of the events, we classify these events into the following 4 groups: (1) events of strike-slip fault type with a common nodal plane parallel to the ENE-WSW striking nodai plane in the fracture zone of the 1984 main shock: (2) events of reverse fault tvpe in the area of the preexisting earthquake swarm to the northeast of the main shock, in a possible relation with an earthquake swarm activated by the main shock; (3) events of reverse fault type that occurred near the largest aftershock t M = 6.2 5. but are not the continued aftershock sequence of the largest aftershock; (4) events of strike-slip fault type at depths to the easternmost part where no activity had been observed before the operation of JSR'86. The plural types of focal mechanisms obtained and the spatial distribution of foci suggest a complex seism o-tectonic structure that consists of at least 2 kinds of fracturings around Ontake Volcano.

Original languageEnglish
Pages (from-to)327-341
Number of pages15
Journaljournal of physics of the earth
Volume40
Issue number2
DOIs
Publication statusPublished - Jan 1 1992
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Earth and Planetary Sciences(all)

Cite this

Yamazaki, F., Ooida, T., Yamada, M., Aoki, H., Fujii, I., Ikami, A., ... Okamoto, T. (1992). Focal Mechanism Analyses of Aftershocks of the 1984 Western Nagano Prefecture Earthquake. journal of physics of the earth, 40(2), 327-341. https://doi.org/10.4294/jpe1952.40.327