Two electrical conductors beneath Kusatsu-Shirane volcano, Japan, imaged by audiomagnetotellurics, and their implications for the hydrothermal system

• Nurhasan

  Department of Earth and Planetary Sciences, Tokyo Institute of Technology

• Ogawa Yasuo

  Volcanic Fluid Research Center, Tokyo Institute of Technology

• Ujihara Naoto

  Department of Earth and Planetary Sciences, Tokyo Institute of Technology

• Tank S. Bulent

  Department of Earth and Planetary Sciences, Tokyo Institute of Technology

• Honkura Yoshimori

  Department of Earth and Planetary Sciences, Tokyo Institute of Technology

• Onizawa Shin'ya

  Volcanic Fluid Research Center, Tokyo Institute of Technology Geological Survey of Japan, AIST

• Mori Takehiko

  Volcanic Fluid Research Center, Tokyo Institute of Technology Geological Survey of Japan, AIST

• Makino Masahiko

  Geological Survey of Japan, AIST

抄録

Kusatsu-Shirane volcano, Japan, is known for its active phreatic eruptions. We have investigated its hydrothermal system by conducting audio-magnetotelluric soundings at 22 stations along a profile that extends across the volcano. The final two-dimensional model is characterized by two conductors. One is a 300- to 1000-m-thick conductor of 1-10 Ωm, which is located on the eastern slope and covered with 200-m-thick resistive layers of Kusatsu-Shirane lava and pyroclastics. This conductor indicates the presence of a Montmorillonite-rich layer of Pliocene volcanic rocks that may function both as an impermeable floor for the shallow fluid path from the peak to the hot springs to the east and as an impermeable cap for the deeper fluid path from the summit region to the foot of the volcano. The second conductor is found at a depth of 1-2 km from the surface, at the peak of the volcano, and its resistivity is as low as 1 Ωm or less. This low resistivity can be explained by fluids containing high concentrations of chloride and sulfate which were supplied from the magmatic gases. Micro-earthquakes cluster above this conductor, and the cut-off of the earthquakes corresponds to the top of the conductor. This conductor infers the presence of the fluid reservoir, and the upward release of these fluids from the reservoir through the conduit presumably triggers the micro-earthquakes at the peak area of the volcano. Crustal deformation modeling using GPS and leveling data of the past 10 years revealed that the center of the deflation coincides with the top of the second conductor, indicating that the fluid reservoir itself can be hosting the deformation.

収録刊行物

• Ｅａｒｔｈ，　Ｐｌａｎｅｔｓ　ａｎｄ　Ｓｐａｃｅ

  Ｅａｒｔｈ，　Ｐｌａｎｅｔｓ　ａｎｄ　Ｓｐａｃｅ 58 (8), 1053-1059, 2006

  地球電磁気・地球惑星圏学会 、公益社団法人 日本地震学会、特定非営利活動法人 日本火山学会、日本測地学会、日本惑星科学会

キーワード

• Resistivity
• volcano
• magnetotellurics
• Montmorillonite
• clay
• fluid

詳細情報

• CRID: 1390001206513720064
• NII論文ID: 10024493633
• NII論文ID: 130003781219
• NII書誌ID: AA11211921
• DOI: 10.1186/bf03352610
• ISSN: 18805981
• ISSN: 13438832
• NDL書誌ID: 8071066
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I8071066
• Web Site: https://link.springer.com/content/pdf/10.1186/BF03352610.pdf
• Web Site: https://link.springer.com/article/10.1186/BF03352610/fulltext.html
• Web Site: http://link.springer.com/content/pdf/10.1186/BF03352610
• 本文言語コード: en
• データソース種別:
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