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  • Letter
  • Open Access

Short-term spatiotemporal variations in the aftershock sequence of the 2004 mid-Niigata prefecture earthquake

  • Aitaro Kato112Email author,
  • Shinichi Sakai112,
  • Naoshi Hirata112,
  • Eiji Kurashimo112,
  • Satoru Nagai112,
  • Takashi Iidaka112,
  • Toshihiro Igarashi112,
  • Yoshiko Yamanaka112,
  • Satoko Murotani112,
  • Tomonori Kawamura112,
  • Takaya Iwasaki112 and
  • Toshihiko Kanazawa112
Earth, Planets and Space201457:BF03352591

Received: 16 February 2005

Accepted: 27 May 2005

Published: 24 June 2014


We deployed 56 temporary seismic stations within approximately a month after the occurrence of the 2004 mid-Niigata prefecture earthquake. Using manually-picked arrival data obtained from the temporary and surrounding permanent seismic stations, 1056 aftershocks have been relocated. Based on the spatiotemporal variations in the relocated aftershocks, the cluster activities associated with the mainshock and some large aftershock events are identified. The aftershocks associated with the mainshock, the largest occurred on the two steep west-dipping planes at an angle of 60° and approximately 5 km away. In contrast, the aftershocks following the event on Oct. 27 are aligned on east-dipping plane at a low angle of 25°. It is further observed that the aftershock area extended in both northeastward and southwestward directions at a later stage. The triggered seismicity around the northeast edge was more significant than that around the southwest edge. This difference could be understood by the discrepancy in the shear stress level accumulated at the dynamic shear rupture due to the mainshock.

Key words

Mid-Niigata prefecture earthquakeaftershocksclusters