Earth, Planets and Space

, Volume 58, Issue 12, pp 1599–1604 | Cite as

Aftershock seismicity and fault structure of the 2005 West Off Fukuoka Prefecture Earthquake (MJMA7.0) derived from urgent joint observations

  • Hiroshi Shimizu
  • Hiroaki Takahashi
  • Tomomi Okada
  • Toshihiko Kanazawa
  • Yoshihisa Iio
  • Hiroki Miyamachi
  • Takeshi Matsushima
  • Masayoshi Ichiyanagi
  • Naoki Uchida
  • Takaya Iwasaki
  • Hiroshi Katao
  • Kazuhiko Goto
  • Satoshi Matsumoto
  • Naoshi Hirata
  • Shigeru Nakao
  • Kenji Uehira
  • Masanao Shinohara
  • Hiroshi Yakiwara
  • Nobuki Kame
  • Taku Urabe
  • Norimichi Matsuwo
  • Tomoaki Yamada
  • Atsushi Watanabe
  • Kazuo Nakahigashi
  • Bogdan Enescu
  • Kazunari Uchida
  • Shin’ichi Hashimoto
  • Syuichiro Hirano
  • Takeo Yagi
  • Yuhki Kohno
  • Tomotake Ueno
  • Masaki Saito
  • Mio Hori
Open Access
Letter

Abstract

On March 20, 2005, a large MJMA7.0 earthquake occurred in the offshore area, west of Fukuoka prefecture, northern Kyushu, Japan. A series of joint observations were carried out by teams from several universities in Japan with the aim of investigating the aftershock activity. Six online telemetered and 17 offline recording seismic stations were installed on land around the aftershock area immediately followed the occurrence of the mainshock. Because aftershocks were located mainly in offshore regions, we also installed 11 ocean bottom seismometers (OBSs) just above the aftershock region and its vicinity in order to obtain accurate locations of hypocenters. The OBS observation was carried out from March 27 to April 13, 2005. We further conducted temporary GPS observations in which ten GPS receivers were deployed around the aftershock region. The aftershocks were mainly aligned along an approximately 25-km-long NW-SE trend, and the hypocenters of the main aftershock region were distributed on a nearly vertical plane at depths of 2–16 km. The mainshock was located near the central part of the main aftershock region at a depth of approximately 10 km. The largest aftershock of MJMA5.8 occurred near the southeastern edge of the main aftershock region, and the aftershock region subsequently extended about 5 km in the SE direction as defined by secondary aftershock activity. Enlargement of the aftershock region did not occur after the peak in aftershock activity, and the aftershock activity gradually declined. The distribution of hypocenters and seismogenic stress as defined by aftershocks suggest that the 2005 West Off Fukuoka Prefecture Earthquake occurred on the fault that is the NW extension of the Kego fault, which extends NW-SE through the Fukuoka metropolitan area, and that the largest aftershock occurred at the northwestern tip of the Kego fault.

Key words

The 2005 West Off Fukuoka Prefecture Earthquake intraplate earthquake mainshock aftershock seismic observation hypocenter distribution active fault Kego fault 

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Copyright information

© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2006

Authors and Affiliations

  • Hiroshi Shimizu
    • 1
  • Hiroaki Takahashi
    • 2
  • Tomomi Okada
    • 3
  • Toshihiko Kanazawa
    • 4
  • Yoshihisa Iio
    • 5
  • Hiroki Miyamachi
    • 6
  • Takeshi Matsushima
    • 1
  • Masayoshi Ichiyanagi
    • 2
  • Naoki Uchida
    • 3
  • Takaya Iwasaki
    • 4
  • Hiroshi Katao
    • 5
  • Kazuhiko Goto
    • 6
  • Satoshi Matsumoto
    • 1
  • Naoshi Hirata
    • 4
  • Shigeru Nakao
    • 6
  • Kenji Uehira
    • 1
  • Masanao Shinohara
    • 4
  • Hiroshi Yakiwara
    • 6
  • Nobuki Kame
    • 7
  • Taku Urabe
    • 4
  • Norimichi Matsuwo
    • 1
  • Tomoaki Yamada
    • 4
  • Atsushi Watanabe
    • 1
  • Kazuo Nakahigashi
    • 4
  • Bogdan Enescu
    • 5
  • Kazunari Uchida
    • 1
  • Shin’ichi Hashimoto
    • 4
  • Syuichiro Hirano
    • 6
  • Takeo Yagi
    • 4
  • Yuhki Kohno
    • 1
  • Tomotake Ueno
    • 5
  • Masaki Saito
    • 1
  • Mio Hori
    • 1
  1. 1.Institute of Seismology and Volcanology, Faculty of SciencesKyushu UniversityShimabaraJapan
  2. 2.Institute of Seismology and Volcanology, Graduate School of ScienceHokkaido UniversitySapporoJapan
  3. 3.Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of ScienceTohoku UniversitySendaiJapan
  4. 4.Earthquake Research InstituteUniversity of TokyoTokyoJapan
  5. 5.Disaster Prevention Research InstituteKyoto UniversityUjiJapan
  6. 6.Nansei-Toko Observatory for Earthquakes and Volcanoes, Faculty of ScienceKagoshima UniversityKagoshimaJapan
  7. 7.Faculty of SciencesKyushu UniversityFukuokaJapan

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