宮城県沖大地震の前兆を捉えるための深層地下水変動研究:2008年2月~2009年12月の観測結果:2008年2月~2009年12月の観測結果  [in Japanese] Studies on deep groundwater changes for detecting the precursors of anticipated large earthquakes off Miyagi Prefecture: Observation results from February 2008 to December 2009:Observation results from February 2008 to December 2009  [in Japanese]

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Author(s)

    • 鹿島 雄介 Kashima Yusuke
    • 東北大学理学研究科地学専攻|現所属:埼玉県新座高校 Department of Geology, Graduate School of Science, Tohoku University|Present address: Niiza High School in Saitama Prefecture
    • 南須原 美恵 Nasuhara Yoshie
    • 東北大学理学研究科地学専攻|現所属:経済産業省 Department of Geology, Graduate School of Science, Tohoku University|Present address: Ministry of Economics, Trade and Industry
    • 中村 隆志 [他] Nakamura Takashi
    • 東北大学理学研究科地学専攻|現所属:東京工業大学情報理工学研究科情報環境学専攻 Department of Geology, Graduate School of Science, Tohoku University|Present address: Department of Mechanical and Environmental Informatics, Graduate School of Information Science and Engineering, Tokyo Institute of Technology
    • 山内 常生 Yamauchi Tsuneo
    • 名古屋大学理学研究科地球惑星科学専攻,現在は停年退職 Department of Earth and Planetary Sciences, Graduate School of Science, Nagoya University, now retired

Abstract

宮城県沖大地震に関連した前兆を検出するため,深層地下水変動観測システムを構築した.本論文で取り扱った2008年と2009年の観測では,2008年5月8日の茨城県沖地震(<i>M<sub>J</sub></i>7.0; <i>M<sub>J</sub></i>は気象庁マグニチュード),同年6月14日の岩手・宮城内陸地震(<i>M<sub>J</sub></i>7.2), 7月19日の福島県沖地震(<i>M<sub>J</sub></i>6.9),および7月24日の岩手県北部沿岸地震(<i>M<sub>J</sub></i>6.8)に関連した水位・水温変動が捉えられた.潮汐に対する観測システムの応答を調べ,3本の孔井の中の2本について,水位換算体積歪を2.27×10<sup>-9</sup>/mm,および0.5×10<sup>-9</sup>/mmと見積もった.水位換算体積歪と理論的な静的体積歪変化から求められた地下水変動の期待値と観測値がよく一致し,地下水変動の要因が静的歪変化であると示唆された.我々の観測システムが地震直後の地下水変動を検知できる下限は,<i>M<sub>J</sub></i>=2.4log<i>r</i>+1.0 (<i>r</i>は震源距離震で,単位はkm)で近似できる.このような式は静的歪変化の距離減衰だけでなく,地震動の距離減衰からも導かれる.

In order to detect the precursors of deep groundwater changes related to the anticipated large earthquakes off Miyagi Prefecture, Japan, we established an observation network of six boreholes with a real-time automatic data-acquisition system. Durning the observation period in 2008 and 2009 groundwater temperatures and levels in three deep boreholes responded to the off-Ibaraki Prefecture earthquake (<i>M<sub>J</sub></i>7.0, Japan Meteorological Agency earthquake magnitude scale) on 8 May 2008, the Iwate-Miyagi inland earthquake (<i>M<sub>J</sub></i>7.2) on 14 June 2008, the off-Fukushima Prefecture earthquake (<i>M<sub>J</sub></i>6.9) on 19 July 2008, and the northern Iwate prefecture coast earthquake (<i>M<sub>J</sub></i>6.8) on 24 July 2008. Examining the responses of our observation system to the earth tides, volumetric strain changes equivalent to water level changes were estimated at 2.27×10<sup>−9</sup>/mm and 0.5×10<sup>−9</sup>/mm for two of three boreholes. Earthquake-related changes in borehole groundwater levels, which were free from the artifacts, are consistent with the estimates from static volumetric strain changes calculated from dislocation models. The lower detection limit of our observation system to co- and post-seismic groundwater changes is approximated by the equation <i>M<sub>J</sub></i>=2.4 log <i>r</i>+1.0, where <i>r</i> represents hypocentral distance in kilometers. Similar equations can be derived not only from the attenuation relation for static strain changes but also from those for ground motion amplitude.

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 117(8), 451-467, 2011

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130001271457
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • ISSN
    0016-7630
  • NDL Article ID
    11223076
  • NDL Source Classification
    ZM49(科学技術--地球科学--地質)
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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