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

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

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)1599-1604
Number of pages6
Journalearth, planets and space
Volume58
Issue number12
DOIs
Publication statusPublished - 2006

Keywords

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

ASJC Scopus subject areas

  • Geology
  • Space and Planetary Science

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