九重火山で観測されたS波の先行相

  • 田中 麻貴
    京都大学大学院理学研究科附属地球熱学研究施設火山研究センター
  • 須藤 靖明
    京都大学大学院理学研究科附属地球熱学研究施設火山研究センター
  • 筒井 智樹
    京都大学大学院理学研究科附属地球熱学研究施設火山研究センター:(現)秋田大学工学資源学部地球資源学科応用地球科学講座

書誌事項

タイトル別名
  • Precedent Phase of S Wave Observed in Kuju Volcano
  • クジュウ カザン デ カンソク サレタ Sハ ノ センコウソウ

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抄録

Kuju Volcano is located in the center of Kyushu Island, Japan. This volcano is a complex volcano formed of andesitic lava domes. A small phreatic eruption occurred at the northeastern side of Mt. Hossho in the center region of the volcano on October 1995. Since then, a seismic network has been installed in this area. Clear precedent phases of S wave are found in many seismograms recorded by the network. Precedent phases show following features; 1) the arrival time difference between the precedent phase and S wave is independent of hypocenteral distance, 2) the phase is significant in a vertical component, 3) the amplitude of the phase is lager than that of P wave, 4) the phase appears for the case of which the seismic station is situated in the direction of relatively large amplitude of S wave from hypocenter. Because of these features, their precedent phases are concluded to be S-P converted phase which is excited in the boundary of S wave velocity. Conversion points distributed within the depth of 0.5 km to 1.5 km from the surface beneath the western region of Kuju Volcano, which are estimated by means of a travel time analysis. Conversion points correspond to a clear boundary of elastic velocity in well data which were obtained around this area.

収録刊行物

  • 火山

    火山 45 (2), 65-73, 2000

    特定非営利活動法人 日本火山学会

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